The State of Server Side Flash Acceleration

Howard MarksChief ScientistDeepStorage, LLC.

Flash in the Server

• Minimizes latency & maximizes bandwidth– No SAN latency/congestion– Dedicated controller

• PCIe flash example– 1.6GB/s bandwidth–>50µs read, >20µs write latency

• But servers are unreliable– Data on server SSD is captive

Server Flash Caching Advantages

• Take advantage of lower latency– Especially w/PCIe flash card/SSD

• Data written to back end array– So not captive in failure scenario

• Works with any array– Or DAS for that matter

• Allows focused use of flash– Put your dollars just where needed– Match SSD performance to application

• Politics: Server team not storage team solution

Server Side Caching Suppliers

• Independent Software Vendors– Proximal Data– PernixData

• Array vendors– EMC – NetApp

• Server vendors– HP– Dell

• Qlogic

• SSD vendors– Intel

• Nevex

– Samsung• Nvelo

– SanDisk • Flashsoft

– Western Digital • sTec EnhanceIO• Velobit Hypercache

– OCZ– Virident

Use Cases

• Database servers– Good fit with shared nothing clusters– Look for OS, SSD support

• Server virtualization– Higher random I/O rates – Look for:

• Dynamic cache assignment• Live migration support

• VDI– Write intensive but captive data less of an issue

Caching Boosts Performance!

Baseline PCIe SSD Cache Low end SSD Cache0

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3500Published TPC-C results

Write Through and Write Back

Baseline Write Through

Write Back0

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TPC-C IOPS

• 100 GB cache• Dataset 330GB grows to 450GB over 3 hour test

Architectures

• Caching software in OS– File or block filter driver

• Caching software in Hypervisor– File or block filter• Vendor may need custom hooks

• Virtual Storage Appliance• Hardware cache device– RAID Controller for DAS– HBA/CNA

Software Caching Locations

Basic Cache Types

• Read• Write Through– Cache populated on write– Data written to back end before ack

• Write Back– Data acknowledged on write to cache–Written to back end storage

asynchronously

Write Back?

• Write back caches speed up writes too

• Data must be protected– Flash is non-volatile – Servers are unreliable– Server crash leads to imprisoned data• Move SSD to new server w/cache software• Flush cache before resume

• Array snapshot issues

Distributed Cache

• Duplicate cached writes across n servers

• Eliminates imprisoned data• Allows cache for servers w/o SSD• Products:– PernixData– Virident– Others soon

• Qlogic FabicCache caching HBA acts as target & initiator

Live Migration Issues

• Does cache allow migration– Through standard workflow

• To allow automation like DRS?

• Is cache cold after migration?• Cache coherency issues• Guest cache – Cache LUN locks VM to server

• Can automate but breaks workflow

• Hypervisor cache – Must prepare, warm cache at destination

Copy Cache During Migration

• Migration includes cache contents

• More data• Extends migration time• Requires new workflow or

hypervisor support• Now available from

ProximalData

Questions and Contact

• Contact info:– Hmarks@deepstorage.net – @DeepStoragenet on Twitter