As presented by Howard at the Flash Memory Summit and silicon valley meetup this presentation is an intro to server side SSD caching. This presentation is an excerpt from our soon to be published report covering this exciting new market segment. For more information on the report please see: http://wp.me/a3A8Hh-7n

1. The State of Server Side
Flash Acceleration
Howard Marks
Chief Scientist
DeepStorage,
LLC.

2. 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

3. 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

4. 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

5. 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

6. Caching Boosts Performance!
0
500
1000
1500
2000
2500
3000
3500
Baseline PCIe SSD Cache Low end SSD Cache
Published TPC-C results

7. Write Through and Write Back
0
10000
20000
30000
40000
50000
60000
Baseline Write
Through
Write Back
TPC-C IOPS
• 100 GB cache
• Dataset 330GB grows to 450GB over 3 hour test

8. 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

9. Software Caching Locations

10. 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

11. 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

12. 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

13. 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

14. Copy Cache During Migration
• Migration includes cache
contents
• More data
• Extends migration time
• Requires new workflow or
hypervisor support
• Now available from
ProximalData

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