iscsi
Post on 30-Dec-2015
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iSCSI
iSCSI Terms
An iSCSI initiator is something that requests disk blocks, aka a client
An iSCSI target is something that provides disk blocks, aka a server.
An iSCSI portal is the combination of the IP and Port of a target
Terms
Target
Portal:172.20.81.5/3260
Linux box, providing adisk as an iSCSI target
Initiator
Windows/Linux/OSX box,Mounting the target asA block device
Terms
In this case, the target is a linux box running the iSCSI daemon. The IP and the port the daemon are listening on are the portal. Any device that can act as an iSCSI initiator can connect to the portal and treat the device as a block device
The space served by the target is a raw disk device
iSCSI Setup
On the server side, setup is still somewhat nasty.iSCSItarget.sourceforge.net has a linux
implementation of iSCSIYou need to recompile the kernel; kernel 2.6 or
more recent is requiredYum update kernel kernel-devel to get the
necessary filesExport KERNELSRC=/usr/src/kernes/2.6.14…Make, make installInit scripts installed in /etc/rc.d, /etc/init.d
iSCSI Target
Target address format:Iqn.2004-04.edu.nps:storage.something.here“iqn” is the type (iSCSI Qualified Name)2004-04 is the date of the first full month the
naming authority was registeredEdu.nps is the reversed domain name, the
naming authorityStorage.something.here is a name assigned by
youBasically, you only have to worry about the last
field
Etc config
In /etc. ietd.conf controls nameTarget iqn.2001-
04.iscsi.ern.ps.edu:storage.iscsi.fileLun 0 Path=/dev/sdb/etc/iscsi has some other config
parameters
Client Side (Initiator)
Now that the target (provider of disk space) is set up we can configure the client.
On Windows, get the MS iscsi initiator (google) and run the installer
Start iSCSI initiator and specify the IP and port to connect to
Discovery/Portals
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Targets
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Note that the namematches the name weprovided in the ietd.conffile--we connected successfully
Disk
At this point we have block device access to the device. On another system I created a FAT filesystem, so we can also show this as a FAT drive.
NOTE: If two machines have block access, they WILL eventually put the FAT filesystem into an inconsistent state. Ditto for ext, zfs, ntfs, and other single-host filesystems
iSCSI on OSX
Supposedly iSCSI was going to be part of Leopard--it didn’t make it. Probably be added at some later date
There are free iSCSI initiators available, http://www.studionetworksolutions.com
Run installer; adds a .kext kernel extension, which requires a reboot
globalSAN
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Note IP and 3260 port
GlobalSan
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Connection established;note match of iscsi ID with that of thetarget config file
Filesystem Creation
Once you have access to the iSCSI drive as a block device, you can create a filesystem on the device.
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Filesystems
Again, conventional filesystems are designed to have only one OS access them as a block device.
We can have multiple hosts contact the iSCSI block device. A conventional filesystem will eventually become inconsistent if you do writes from multiple hosts
What did we get?
We accessed a block device on a linux server from OSX and Windows across an IP network using commodity ethernet (or wireless) protocols.
This isn’t quite a SAN, since we don’t have volume management, but it provides the substrata needed for that
Volume Management
This is somewhat tricky and still a developing field. There are a number of commercial implementations and a few open source implementations
This is the layer that handles concurrent access to block devices
Architecture
What would a cluster architecture look like with a SAN?
iSCSI devices
No endorsement implied by any mention of a vendor, prices variable….
Promise vtrack: ~$5K for enclosure, plus disk
16 SATA bays, 3U, RAID, TCP Offload Engine
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iSCSI Devices
HP Storage Works AIO 1200, 600, 400SATA or SAS drives possiblehttp://h18006.www1.hp.com/storage/aiostorage.html?jumpid=reg_R1002_USEN~ $8K for 3 TB
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iSCSI
Sun is generally dismissive of iSCSI for their enterprise storage products
EMC has an installed base in FC, though they do offer iSCSI in parallel on some boxes
EMC is partnered with Dell: AX150 (12 SATA drives, 9 TB, RAID) $11K for 1.5TB (Massive discounts probably apply)
CX3 series: up to 144TB, enterprise stuff
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