Download - Fundamental Og Well Built SAN-4AA2-5616ENW
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
1/15
Fundamentals of a W ell-Built SAN
W hite paper
Table of contents
Introduction..................... .................. .................. .................. .................. .................. ................ .......... 2Executive summary................. .................. .................. .................. .................. .................. .................. .. 2Anatomy of a SAN ................ .................. .................. .................. .................. .................. .................. .. 3The advantages of iSCSI SANs ................. .................. .................. .................. ................. .................. ... 3Core features of HP LeftHand SANs................. .................. .................. ................. .................. ............... 3
True clustering ................ .................. .................. .................. .................. .................. .................. ..... 4Storage virtualization .................. .................. .................. .................. .................. .................. ........... 4Reliability with Network RAID............. .................. .................. ................. .................. .................. ...... 5Continuous data availability...... .................. .................. .................. .................. .................. .............. 5Scalable capacity and performance.......... ................. .................. .................. .................. .................. 5Easing administration overhead................ .................. ................. .................. .................. .................. 5Enhanced data services...... .................. .................. .................. .................. .................. .................. .. 5HP Services................. .................. .................. .................. .................. .................. .................. ........ 5
Scalable performance .................. .................. .................. .................. .................. .................. .............. 6Scalability by design ................ .................. .................. .................. .................. .................. .............. 6Limitations of traditional architectures..... .................. ................. .................. .................. .................. ... 6Objective scalability measures........................... .................. .................. .................. ................. ......... 7Flexible scalability models.................. .................. .................. .................. .................. .................. ..... 8Scaling with tiered storage........ .................. .................. .................. .................. ................. ............... 8
High availability..... .................. .................. .................. .................. .................. .................. ................ . 9Synchronous replication and disaster recovery with multi-site SANs........ ..... .... ..... .... ..... .... ..... .... ..... .... ... 9
Reliability by design...... .................. .................. .................. .................. .................. .................. ......... 10 Building reliability from the ground up ............... .................. .................. .................. .................. ....... 11
Extreme performance................ .................. .................. .................. .................. .................. ............... 13 Performance through parallelism...... .................. .................. .................. ................. .................. ....... 13 Increasing parallelism and performance with MPIO DSM .................. .................. .................. ............. 13 Increasing bandwidth dramatically........................ .................. .................. ................. .................. .... 14 Investment protection ................ .................. .................. .................. .................. .................. ............ 15
Conclusion............. .................. .................. .................. .................. .................. .................. ............... 15 For more information.......................... .................. .................. .................. .................. .................. ...... 15
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
2/15
Introduction
Next to its people, data is a companys most valuable asset. Businesses of every size rely heavily on
data that is at once increasingly complex and increasingly regulated. In countries around the world,
government regulations dictate how financial, customer, personnel, and health-related information is
stored, maintained, and retained.
Central data storage and management help organizations achieve compliance with this mountain of
requirements, and help enable business-critical data to be available when users need it. Storage areanetworks, or SAN s, are common solutions for businesses seeking to simplify storage. Unlike direct
attach storage (DAS), which creates disparate, random islands of information, SAN s centralize data
storage. Disaster recovery solutionsa necessity in todays worldare easier to implement on SAN s,
and the stored data is easier to manage than in a DAS environment.
A company that leverages server virtualization for high availability and disaster recovery has even
more reason to deploy a SAN and not just any SAN . Virtualized environments need shared storage
to take full advantage of the shared infrastructure. W hen both server and storage are protected, the
solution is complete.
Although Fibre Channel SANs are an option for large enterprises, these storage solutions tend to be
expensive and limited in their flexibi lity. Compact and cost-effective, iSCSI SAN s are a better fit for
many businesses. HP LeftHand iSCSI SAN solutions are built in a fundamentally different way. Built
from the ground up to be flexible, scalable, and highly avai lable, HP LeftHand P4000 SANs deliver
all of the features of enterprise storage and are an excellent fit for disaster recovery, business
continuity, and virtualized storage solutions.
Executive summary
Your businesss increasing reliance on data calls for a well-designed and well-built data storage
system. Agile, easy to deploy, and intuitive to manage, HP LeftHand P4000 SAN Solutions provide
all of the functions that organizations expect to see in a Fibre Channel SANat an affordable price
point that makes centralized storage an economical option even for small- and medium-sized
businesses. In fact, HP LeftHand SANs enable high avai lability and lower cost 49% in small sites and
remote offices by turning internal server drives into shared storage1 . And, because HP LeftHand SANs
are built with a superior architecture, they are more scalable and offer higher availability, more
reliability, and higher performance than other iSCSI SAN products.
HP LeftHand SAN s are based on iSCSI technologySCSI over standard Internet protocols (IP). This
allows companies to use the standard iSCSI drivers that accompany server operating systems to
access storage over standard IP networks.
HP LeftHand SANs use a process called true clustering. True clustering means that every storage
system in a cluster participates equally in sharing both the clusters workload and storage capacity.
The cluster manages itself. W ith true clustering, organizations can administer a single entity while
configuring virtual volumes and per-volume Network RAID levels. They can also take snapshots, makeremote copies, scale the cluster, and even take storage systems down for upgrades or maintenance
all without affecting data availability.
HP LeftHand SANs deliver the enterprise storage management features that companies expect of Fibre
Channel SANs. However, the similari ty ends there. The purpose of this white paper is to describe the
benefits of a clustered architecture in comparison with traditional controller-based architectures, and
to discuss the technology that makes HP LeftHand SAN s better by design.
1 Based on US list price comparison on July 1st, 2009 between a 4TB dual-controller Dell EqualLogic PS6000 and HP P4000 VSA Software plus
24 250GB HDDs used to create the virtual iSCSI SAN in a VMware deployment.
2
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
3/15
Anatomy of a SAN
Every SAN is deployed using a combination of software, hardware, and services. In this respect,
HP LeftHand SANs are no different from any other SAN . W hat make them different are the
advantages they provide in all three of these areas. HP LeftHand SAN s run powerful HP SAN / iQ
software, clustering multiple storage systems into a single SAN that you can manage from a central
console. They operate on enterprise-class, industry-standard, x86-architecture-based hardware
equipped with advanced disk drives, processing elements, caches, and controllers. Finally, HP
provides support and service that keeps customer data available and protects it from loss.
The advantages of iSCSI SANs
As they evaluate technologies, many organizations choose iSCSI SAN s because of the complexity
and costs of tradi tional Fibre Channel (FC) SAN s. Installing a traditional FC SAN means purchasing
storage hardware years ahead of the need. This costly, buy high, sell low proposition is ampli fied
by ever-plummeting storage costs. The cost of a pair of redundant FC host bus adapters (HBAs), which
can approach that of a small server, impedes the use of centralized storage for all servers.
Growing a Fibre Channel SAN that uses the traditional model of a hardware RAID controller
connected to multiple disk trays has its limits: as the number of disk trays increases, the controller itselfbecomes a bottleneck, requiring the purchase of more complete storage systems. And as 2Gb/ s to
4Gb/ s FC throughput is eclipsed by off-the-shelf 10Gb/ s Ethernet (10GbE), the perception that a FC
fabric delivers better performance than iSCSI is fast becoming obsolete.
Core features of HP LeftHand SANs
HP LeftHand SAN s aggregate the resources of a set of enterprise-class storage systems into a storage
cluster. The result is flexible, scalable, virtualized storage (see Figure 1). The benefits of this
technology are discussed in the following sections.
3
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
4/15
Figure 1: HP LeftHand P4000 SAN s are comprised of enterprise-class storage systems. The physical blocks in the SAN
corresponding to virtual volumesare distributed evenly across the cluster.
True clustering
P4000 SAN s provide true, n-way clustered storage, not a traditional two-way active/ active or
active/ standby configuration. True clustered storage means that a set of storage systems is managed
and scaled as a single entity, with all of the clusters resources available to respond to requests. As
the cluster is expanded, the resources available to handle requests increase as wellalleviating the
problem of a controller bottleneck, which is commonplace when traditional SANs are scaled.
Storage virtualization
True clustering creates a virtual pool of storage, spreading the storage for its virtual volumes evenly
across all storage systems in the cluster. Storage can be reserved at the time that the virtual volumes are
createdor, through thin provisioning, it can be allocated only as disk blocks are actually needed.
HP LeftHand SANs virtualize every volume across all the storage systems in a clusternot within each
storage system, as do traditional Fibre Channel SANs. The sharing of storage across the entire clusterresults helps increase performance and storage utilization; in addition, it helps decrease management
costs and complexities as clusters are scaled.
4
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
5/15
Reliability with Network RAID
The reliability of HP LeftHand SANs begins with RAID storage on each storage system. It is then
enhanced wi th Network RAID, which replicates each block across the storage cluster up to four times.
W hen a virtual volume is populated, i ts data blocks are striped and replicated across the clusters
storage systems so that the entire cluster participates in the storage of every virtual volume.
Continuous data availability
Network RAID contributes to high availability, helping to ensure that the loss of a single storage
system does not result in data loss. If a server fails to the point where it must be taken offline for
repair, N etwork RAID keeps the single server failure from resulting in loss of data avai lability. W hen
the server is replaced, or repaired and brought back online, the SAN automatically brings the storage
systems data blocks up to date with the rest of the cluster.
The more storage systems there are in a cluster, the less the failure of a single storage system can
affect performance. A traditional active/ active dual-controller SAN product can suffer a 50%
performance decrease in the event of a controller loss. W ith P4000 SAN s, the failure of a storage
system affects performance by, at most, a percentage equal to the proportion of the cluster that the
storage system represents.
Scalable capacity and performance
As a cluster becomes full, storage capacity can be increased by adding storage systems. True
clustering enables considerable scalabi lity. As new storage systems are configured, the cluster
automatically readjusts its block allocation so that the allocated storage and the workload are once
again distributed across the cluster. This procedure immediately scales the clusters performance by
bringing incremental network CPU, memory, cache, RAID controller, and disk resources to the cluster.
Easing administration overhead
All storage clusters are managed through a single, intuitive centralized management console (CMC).
The ability to treat a storage cluster as a single entityrather than a set of discrete storage devices
eases administration costs and changes the cost model from one in which storage must be plannedand purchased upfront to one in which it can be purchased as needed.
Enhanced data services
In traditional SAN s, enhanced data services are typically add-on features. W ith HP LeftHand SANs,
enhanced data services are included at no additional charge. Synchronous replication keeps data
highly available within a cluster, even if that cluster is geographically separated between sites in a
LAN or MAN . Remote copy provides disaster recovery for multiple clusters and sites from a single
interface, and failover and failback are automated features. The unique allocate-on-write thin
provisioning provides the ability to create volumes without dedicating physical storage to them.
Snapshots are space-efficient because they are thinly provisioned.
HP Services
HP LeftHand SAN s are supported by global, world-class enterprise-support services. This can be a
significant advantage for data centers already engaged with HP. Companies may already have
spares on site, they may already know their support technician, and the technician may already be
badged for the site and familiar with its best practices. The size and skill set of the available
hardware support from HP also helps organizations compete.
5
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
6/15
Scalable performance
Scalability means that adding more resources to a system results in a commensurate increase in the
systems ability to perform work. HP LeftHand SANs use true clustering to deliver a SAN that scales both
storage capacity and performance in a linear manner. Scaling a cluster with additional storage systems
supports growth by scaling existing volumes, adding new volumes, and supporting more servers (Figure 2).
Scalability by design
HP LeftHand SANs are designed to deliver massive scalabi lity. Unlike other clustered storage
products, P4000 SAN s have no bui lt-in limit on the number of storage systems per cluster. Because
true clustering allows them to scale performance and capacity linearly, HP LeftHand SANs differ from
traditional Fibre Channel SAN products.
HP LeftHand SAN s are based on HP ProLiant servers, each of which has its own disk drives, RAID controller,
cache, memory, CPU, and networking resources. Thus, each time a new storage system is added to a cluster,
the clusters processing capacity increases in lock step with its storage capacity. The SANs linear scalability
derives from the fact that the ratio of processing resources to disk storage is constant.
Figure 2: HP LeftHand SANs use true clustering to deliver linear scalability that can support more storage capacity and
performance as the cluster grows.
Limitations of traditional architectures
Compare this scalabili ty model to the traditional controller/ disk tray architecture that is behind most Fibre
Channel SANs and some NAS appliances (Figure 3). These systems use either an active/ active or an
active/ standby pair of processors, and scalability is achieved by adding more disk trays to the
configuration, as more capacity is needed. Using this model, the ratio of processing power to disk
capacity decreases each time a new disk tray is added to the configuration. This causes performance to
increase to the point where the controllers and the Fibre Channel interconnect become a bottleneck;
performance then levels off or even declines. At that point, customers must either upgrade to higher-power
controllers or add new storage systems. Either action can result in significant amounts of downtime.
6
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
7/15
Figure 3: A traditional SAN architecture scales by adding more disk trays to the configuration.
Objective scalability measures
ESG Lab, part of the Enterprise Strategy Group, measured scalability of HP LeftHand SANs of varying
sizes, and summarized the results in a July 2007 report2 . The test cluster consisted of an HP LeftHand
SAN configured wi th up to 30 HP ProLiant DL320 Servers. Each server was configured with 12
300GB, 15k rpm serial-attached SCSI (SAS) drives, yielding a total of 3.6TB of storage per server.
ESG used the IOMeter benchmark to drive a simulated online transaction processing workload
consisting of 60% read and 40% write operations, using 8KB blocks. Scalability was nearly linear
from five to 30 storage systems, and the 30-server, 108TB cluster was able to sustain almost 50,000
input/ output operations per second (IOPS).
HP LeftHand SANs allow organizations to build clusters whose characteristics are tuned for the
applications they support, scaling each cluster as needed. Many organizations deploy their first
open iSCSI SAN to support specific applications such as Microsoft Exchange Server, VMware
Infrastructure 3, Microsoft SQL Server, and network file sharing. As they begin to see the benefits ofHP LeftHand technology first hand, they scale their cluster to support more and more applications
(Figure 4). As these applications become more diverse in their storage requirements, it often makes
sense to create a new cluster with a different type of storage system as its basis. Both clusters can
scale independently, and logical volumes can be moved between clusters with no interruption in
service. This makes scaling with tiered storage easy and straightforward.
2 LeftHand N etworks 100 TB Enterprise SAN.
7
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
8/15
Figure 4: Network RAID level 1 stripes and replicates a logical volumes data across the cluster.
Flexible scalability models
HP LeftHand SANs scale capacity as well as performance. Organizations can increase the storage
capacity of a cluster by adding new storage systems, and they can even scale clusters with non-
identical storage systems. Scaling a cluster to 100 storage systems is as simple as scaling to two. In
addition to scaling the size of a cluster, companies can create multiple clusters because the cluster is
managed as a single unit.
Multiple SANs are configured in a single management group by the centralized management console
(CMC), which provides a single, intuitive graphical user interface (GUI) to manage them. Logical
volumes can be copied between clusters with a simple click of the mouse. Given the fact that
management groups can span geographical distances, remote copy works as simply and easily as a
local copy does between clusters.
Scaling with tiered storage
Different types of disk drives have di fferent performance characteristics, and these characteristics
affect storage system performance and thus overall SAN performance. SAS and SCSI drives tend to
have high rotational speeds and low seek times, resulting in low I/ O latency and therefore high
input/ output operations per second (IOPS). Storage systems using SAS drives excel in supporting
transactional applications such as databases and Microsoft Exchange servers. Serial ATA (SATA)
drives tend to have lower rotational speeds and higher latency, but much higher capacity for the price
than SAS and SCSI drives. Clusters built around these storage systems are more cost-effective for
applications that demand high capacity, such as streaming media and general file storage.
8
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
9/15
High availability
Availabili ty is about keeping data online and available at all times, an attribute that is typically
attempted by using redundant components. But what happens if multiple components fail within a
unit, or the entire unit becomes unavailable?
The HP LeftHand P4000 SAN has redundant components such as redundant power supplies and
hardware RAID 5, 6, and 10. But, to achieve true high availability, volumes must remain online
whether a drive fails or the entire unit becomes unavailable. Network RAID provides this capability atno extra charge.
Network RAID levels are assigned on a per-volume basis so that avai lability can be configured based
on the needs of individual applications and their data. This allows organizations to incur the cost of
redundant storage only for logical volumes that require it.
HP LeftHand SANs support striping plus Network RAID replication levels 0, 2, 3, and 4, which
correspond to replicating each block up to four times. The most commonly configured Network RAID
level, level 2, stripes and replicates blocks so that two copies of each block reside on the cluster
(Figure 4). Using this configuration, the logical volume continues to be available despite the failure of
a single storage system or the failure of two non-consecutive storage systems. Compare this to
products that stripe without replication: the more storage systems in a cluster, the lower the
availabilityand the loss of a single storage system means that all storage is lost.
In HP LeftHand SANs, clusters manage data layout and replication themselves so that failover is
automatic and so is failback. If a storage system fails and is later brought back online, the cluster
manages the process of restoring the repaired servers data to the current level. Likewise, N etwork
RAID level is a property of a logical volume that can be changed at any time. If the level is changed,
the cluster manages the process of increasing or reducing the replication level of data for the logical
volume as required.
Synchronous replication and disaster recovery with multi-site SAN s
The availability properties of Network RAID mean that functionality such as synchronous replication
and disaster recovery is built into the solution. This simplifies administration, helps to protect data, andreduces costs compared to tradi tional SAN s.
Volumes stored with Network RAID level 2 have blocks striped across every other storage system, with
replicas stored across the rest. Logical volumes continue to be available even if half the systems in the
cluster fail.
Synchronous replication to provide multi-site high availability can be implemented simply by placing
half the storage systems in one location and the rest in another. W hether the alternate location is a
different closet in the same building, another building on the same campus, or a data center far
away, blocks are synchronously replicated across the two sites, and an entire site can fail without
making any data unavailable (Figure 5).
W hen the failed site comes back online, its storage systems automatically obtain any changed blocks
so that failback is automatic and transparent. With traditional SANs, this process can be time-
consuming and error-prone, and it can require application downtime.
9
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
10/15
Figure 5: Placing alternate storage systems in different, alternate locations enables synchronous replication and disaster
recovery as natural side effects of HP LeftHand SAN storage.
Reliability by design
Reliability is about protecting against data loss, which is a considerable proposition given the forward
march of disk technology. Disk reliability is typically expressed in terms of bit error rate (BER), which
means that disks may fail as a function of the amount of data read or written. As disk technology
allows drives to contain more data, they are more likely to fail when read from beginning to end; this
is exactly what happens during a RAID array rebuild after a single-disk failure.
The upward trend in disk sizes means that the dreaded second-disk fai lure that incapacitates a RAID 5
array is becoming more likely as disk sizes increase. Indeed, the chance of a second disk failure
while rebuilding a 9TB RAID array of SATA disk drives is nearly 10%greater than the probability of
a dual controller failure in a traditional SAN . RAID 5 by i tself is no longer sufficient. The reliabili ty by
design of the HP LeftHand SAN allows organizations to configure logical volumes and clusters to
provide higher reliabili ty levels.
10
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
11/15
Building reliability from the ground up
Reliability is built into every HP LeftHand SAN, from the choice of storage systems to the additional
features that help organizations better manage their data.
Hardware features: Every component in an HP LeftHand SAN includes dual power supplies, network
interface cards (NICs), environmental monitoring, and a battery-backed-up write cache.
Choice of drives: The HP LeftHand SAN offers storage options that allow customers to choose the
combination of performance, capacity, and reliability that best suits their applications. Enterprise-class
SAS and SATA drives offer reliability levels equivalent to the Fibre Channel drives found in traditional
SAN s, with a BER of 1/ 1016. W here capacity and price are more important than this level of
reliabi lity, SATA drives can deliver a BER of 1/ 1014.
Hardware and Network RAID: Each storage system has built-in hardware RAID and battery-backed-up
write cache, both of which contribute to reliability and data protection. Depending on the system and
customer requirements, hardware RAID levels 5, 6, and10 can be configured on each storage system
and then combined with Network RAID levels to maximize availability.
Proactive self-healing: Just like traditional Fibre Channel SAN s, HP LeftHand SANs monitor storage
systems for marginal environmental or drive condi tions, allowing an HP LeftHand SAN to respond
with proactive support services, repairing potential faults before they result in an actual failure. Each
storage system is constantly scrubbing its storage to re-map bad blocks and restore data from astorage system that has an intact replica.
Geographic failover: Many organizations view the potential loss of data and application downtime
due to the failure of an entire data center as unacceptable. Network RAID allows for synchronous
replication and geographic failover so that business can continue without interruption. As discussed in
the Synchronous replication and disaster recovery with multi-site SANs section, synchronous
replication is integrated into the superior architecture of HP LeftHand SANs. W hats more,
organizations can purchase an HP P4300 SAS Starter SAN for the price that some vendors charge
for their remote replication software alone. And, unlike the competitions remote replication software,
failover and failback are not applicable to a HP LeftHand SAN because storage volumes remain
online and accessible throughout a site failure.
Space-efficient snapshots: Every organization knows that there is no substitute for stable, offline tapebackups. HP LeftHand SAN s support space-efficient snapshots where only the metadatanot the
blocks themselvesis copied to create the snapshot. Space efficiency means that the storage system
does not have to reserve an amount of storage for the snapshot equivalent to the size of the volume
itself. Space efficiency results in significant savings compared to traditional SAN s.
Scheduled snapshots can be coordinated wi th application software so that the snapshot represents a
stable point-in-time copy of application data. In contrast to traditional SAN s, snapshots in HP LeftHand
SANs can be mounted and written to by the backup software.
Snapshots may also be created manually and used to create temporary environments for developers
and administrators. Software upgrades and patches, for example, can be applied and tested to a
volume snapshot and tested on a real server or in a virtual machine before they are put into
production. Costs for these snapshots are low because an equal amount of additional storage does
not have to be available in order for the snapshot to be taken.
Remote copy and asynchronous replication: The snapshot mechanism in an HP LeftHand SAN forms
the basis for remote copy and asynchronous replication capabilities. Snapshots contain an identifier
that ensures uniqueness within a management group. Snapshots can be copied between clusters,
promoted to be actual volumes, and then mounted and used. W hen clusters are geographically
separated, a local copy becomes a remote copythere is no difference.
11
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
12/15
Consider an organization with data centers in Seattle and San Francisco, with New York acting as a
central data repository for backups or as a disaster recovery site (Figure 6). Snapshots can be created
in Seattle and San Francisco, copied to New York, and then promoted to be fully populated volumes.
Servers C and D, the users of the promoted snapshots, could represent hot standby servers for
disaster-recovery purposes, or they could be used to handle tape backup of the copied volumes.
Figure 6: Remote copy is based on the snapshot mechanism, and it can be used for disaster-recovery and
remote-archiving purposes.
HP LeftHand SANs support scheduled snapshots and remote copies. Used in combination, these two
capabilities provide asynchronous replication, where batches of data representing the difference
between two snapshots are created and transferred between sites on a periodic basis.
Reliability is about protecting against data loss every step of the way, from establishing a per-server
reliabi lity baseline to supporting geographic fai lover and failback capabi lities. HP LeftHand SANs
provide flexible reliability at a price point that makes them superior to traditional SANs.
12
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
13/15
Extreme performance
The disk spindles performance characteristics ultimately drive disk storage system performance. O ne
challenge facing vendors of storage systems is how to extract the most performance from them.
In contrast with traditional SAN s, HP LeftHand SANs excel at extracting top performance from storage
systems. Companies that use HP LeftHand SANs experience the high performance and capacity of the
latest disk drivesstandard in the HP ProLiant servers on which LeftHand SAN s are basedlong before
those drives are avai lable in traditional SAN architectures. In addition, HP LeftHand SANs leverage theunderlying hardware to extract an uncommon level of performance from the hardware itself.
Performance through parallelism
Most SAN s increase storage system performance through parallelism. HP LeftHand SAN s allow
organizations to tune the level of parallel operations in their cluster to achieve required
performance levels.
Performance begins with RAID storage on each storage system, which uses parallel disk operations to
deliver high I/ O bandwidth. Even though RAID 5 is the default configuration, higher and lower RAID
levels can be configured to adjust both performance and protection. For example, RAID 10 can be
configured for higher performance requirements, and RAID 6 can be configured to protect against
multiple drive failures.
A level above RAID on the individual storage systems, the cluster itself contributes to performance by
striping dataregardless of N etwork RAID levelacross the entire cluster. Just as RAID on the storage
systems delivers the performance of disk drives working in parallel, Network RAID on the cluster itself
delivers the performance of multiple RAID arrays delivering data in parallel. Striping across multiple
storage systems is managed by the cluster itself, so administrators can manage only a single entity
rather than a set of individual storage systems.
Compared to tradi tional SAN s, where the controllers themselves become a bottleneck as more disk
trays are added to a system, HP LeftHand SAN performance grows as storage capacity grows. This is
because each time a new set of disks are added to the cluster, they are supported by an additional
set of resources, including: CPU and main memory for managing storage, I/ O, and the cluster Hardware RAID controller per storage system Additional battery-backed-up storage for each storage system Additional network interfaces that can operate in parallelIncreasing parallelism and performance with MPIO DSM
By default, an HP LeftHand SAN load-balances initial login requests from client iSCSI drivers across
the storage system, and then processes all subsequent requests from that client through a single
storage system. The storage system redirects each client request to the server owning the desired
block, and then redirects the response back to the client. Although this approach results in excellentscalability, it is not as scalable as the performance that can be achieved with the HP LeftHand device-
specific module (DSM) for the Microsoft Windows Multipath I/ O (MPIO) iSCSI driver.
The MPIO DSM contains intelligence on the layout algorithms for the storage cluster. It can thus
calculate the location of any block in any virtual volume. Knowing which server contains the desired
block allows the iSCSI driver to contact the storage system that owns the block directly, without the
redirection used by the standard load-balancing approach. Figure 7 illustrates a redirected login
sequence, the SCSI mode sense command that loads the cluster-specific information into the driver,
and the separate I/ O path that the driver establishes to each server in the cluster.
13
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
14/15
Figure 7: The HP LeftHand SANs device-specific module for the M icrosoft MPIO driver (MPIO DSM) increases performance by
establishing parallel I/ O pathsone to each storage system in the cluster.
The MPIO DSM provides the most benefit wi th sequential I/ O. Performance scalability for standard
load balancing is excellent. However, as the volume of data increases, the load that redirection
imposes on the network increases as well. MPIO DSM eliminates the additional data movement and
allows data to stream directly from storage systems to the client systems. W here the benefits of larger
clusters for standard load balancing begin to diminish, the MPIO DSM configuration allows
performance to continue to climb significantly higher as storage systems are added to the cluster.
Increasing bandwidth dramatically
Most storage systems are limited in bandwidth. In traditional SANs, once storage capacity is
increased to the point where the systems controllers can no longer provide increased bandwidth
along with increased capacity, customers either must upgrade controllers or purchase additional
storage systems. Multiple traditional storage systems add not only cost but also complexity. They also
need to be managed individually with volumes statically allocated to each system, resulting in
fragmentation. In contrast, a storage cluster can virtualize storage across the entire system.
14
-
8/6/2019 Fundamental Og Well Built SAN-4AA2-5616ENW
15/15
Investment protection
The industry standard, enterprise-class x86-architecture in an HP P4000 SAN offers unprecedented
investment protection for organizations. For example, they can repurpose existing storage servers as
application servers and, using the HP P4000 Virtual SAN Appliance (VSA) Software, provide SAN
storage on them as well. In small sites and remote offices, HP LeftHand SANs enable high availabi lity
and lower costs 49% by turning internal server drives into shared storage.
Investments in HP LeftHand SAN s continue to be protected through the transition to 10 -Gb/ s Ethernet
(10GbE). Customers can upgrade existing clusters in the field with standard 10GbE interfaces andconnect to standard PCI Express peripherals. Redundancy built into the underlying platform allows
them to upgrade to a live cluster without impacting data availability.
Unlike traditional SANs, each storage system in a cluster contributes to performance by delivering
data in parallel. So deploying a cluster with 10GbE provides improved throughput, which is then
enhanced further when that throughput is multiplied by the number of storage systems in the cluster.
Conclusion
Every SAN is built from a combination of software, hardware, and services, and in this respect iSCSI
SAN s from HP are no different from any other SAN . But that is where the similarity ends. HP LeftHand
SANs use distributed, clustered technology to deliver all of the functionality expected of a storage
area network. They add the advantage of l inear scalabili ty, high availabili ty, per-logical-volume
configured reliability, and throughput of 10-Gb/ s per node that is aggregated between all nodes in a
cluster. Better by design, HP LeftHand P4000 SANs deliver functionality including synchronous
replication, asynchronous replication, and remote copy. These are built-in features of a superior
architecturenot an add-on option that can cost as much as an entire SAN.
W ith true clustering, HP LeftHand SANs can virtualize storage across all storage systems in a cluster
and even between clusters in the same management group. True clustering allows organizations to treat
a cluster as a single entity whose resources can be scaled and configured as needed. This helps deliver
the unique combination of performance and reliability that each application in a data center requires.
For more information
For more information on HP LeftHand iSCSI SAN s, visit www.hp.com/ go/ P4000.
Technology for better business outcomes
Copyright 2009 Hewlett-Packard Development Company, L.P. The informationcontained herein is subject to change without notice. The only warranties for HPproducts and services are set forth in the express warranty statementsaccompanying such products and services. Nothing herein should be construed asconstituting an additional warranty. HP shall not be liable for technical or editorialerrors or omissions contained herein.
Microsoft and W indows are U.S. registered trademarks of Microsoft Corporation.
http://www.hp.com/go/P4000http://www.hp.com/go/P4000http://www.hp.com/go/getconnected