why flash storage caching
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Storage CachingTim Fletcher
Brighter Connections
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Who are we?
15+ year Linux experience13 years work in educationRHCE since 1999 (RedHat 6.1)
Joined Brighter Connections in OctoberIT Practise in HuddersfieldSpecialise in innovative solutions
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Why your SAN is slow
Centralised storage, good for cost bad for performance
Lots of different competing workloads mean disks "thrash"
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Making your SAN faster
HardwareSpindlesRAM
SoftwareCopy on WriteQuality of Service
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Hard Drives
Technology basically the same for over 30 years, known as "Spinning Rust".
Good for cheap bulk storageGood at linear access
Bad at random accessPower hungryFragile
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Memory
Very fast accessVery good random accessDirectly connected to the CPU
ExpensiveVolatilePower Hungry
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Flash
Very fast, especially at random accessCan be connected directly to the PCI-e busNon volatileLow powerMassive drops in price, but still expensiveCells can wear outIncludes firmware
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Storage Speeds
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PCIe vs Hard disk emulation
Hard disk emulationEasy to deployWell understoodCheapMany layers of translation
PCIeExpensive, or is it?Higher power drawDirectly attached to the CPU bus
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Caching - Why does it matter
Flash is expensive and wears outThe closer the data is to the CPU the betterKeep your SAN arrayLeverages the best of both worlds
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Caching - Where do your blocks go?
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Flashcache
Fully open source, released by FacebookKernel module, based in the device mapper layerStarting to appear in distrosError resistantCache can be added and removed from storageUsed by Facebook in production
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Bcache
Fully Open SourceDesigned from the ground up to cacheDesigned with an understanding of flashHigher performance
Requires devices to be rebuilt as "bcache" devicesRequires full kernel rebuild
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ZFS
Not just a filesystemIncludes device management, RAID and filesystem management.Open Source but license incompatible with GPLWritten by Sun, available in FreeBSD, Solaris derivatives, and LinuxCan use SSDs as L2ARC and as SLOGCache devices can be live added and removedCache does not persist over reboots
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Closed Source Options
Hook in to VMware
FusionIO - ioTurbineSanDisk - FlashSoft
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Questions?tim@brighter-connections.comwww.brighter-connections.com
@timjdfletcher