The state of server side caching
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Transcript of The state of server side caching
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:– [email protected] – @DeepStoragenet on Twitter