CLARiiON FAST Cache #emcworld

  • Available later this year (2010)
  • Aligned with FAST: “Place data on the most appropriate storage resources”
    • Temporarily relocates often-used data to faster storage resources
      • Provide Flash drive performance to hottest data
      • Reduces load and improves performance of other resources
    • Fully automated application acceleration
  • Performance proposition
    • Large enough to contain a high percentage of working set over long time intervals
    • Fast enough to provide order of magnitude performance improvements
  • Traditional DRAM cache vs FAST cache
    • DRAM cache limited in size and very fast 10^-9
    • 15K FC disk drive 10^-3
    • Flash drive 10^-6
  • Requirements
    • FLARE R30 Required for FAST Cache
    • Dedicated FLASH drives
    • Native mirrored protection for read/write cache
    • Can be unprotected for read cache only
  • Implementation
    • Memory map tracks host address usage and ownership
      • 64kb extents (not LUN movement, much more granularity)
    • All I/O flows through the FAST cache driver and memory map
      • Memory map lookup is very low impact
      • Memory map does take some DRAM space so there will be marginally less DRAM cache available (~ 1 GB of DRAM per 1 TB of FAST Cache)
    • No “FORCED FLUSHING” so for bursty work loads that invoke traditional DRAM forced cache flushes this may help.
    • Background process runs on CX to cleanup the extents
  • Benefits
    • Flash Cache read hits = Flash drive response times
    • Flash Cache write hits flush faster
    • Flash Cache hits offload HDDs
    • Lower net application response time enables higher IOPs
    • Efficient use of Flash drive technology
  • Key concept for max Flash cache benefit
    • Understand Locality of Reference
      • Total GB of actively reference data
      • Same areas reference over short periods and multiple times
  • What makes for a good Flash cache workload
    • Small to moderate working sets
    • High frequency of access to same chunks – rehits
    • Perf limited by disk technology not SPs
  • Profiles of common apps
    • DB OLTP/DSS
      • Oracle, MS SQL
    • Exchange
    • File Servers
  • Determine appropriate subset of LUNs for use with Fast cache

Note:  Sequential workloads are still (typically) better served by traditional rotational media  (e.g. – backup-to-disk)

  • Tools
    • FAST cache analyzer
      • Will require RBA traces for FAST cache analysis
  • Uber tiering with FAST cache plus FAST
    • DRAM cache  <-> FAST cache <-> FC <-> SATA
  • FAST Cache is a license so the CX enabler will be required (there is a bundle for both FAST and FAST cache)

Questions:

  • Are you limited to 2 TB FAST cache?  Can you have multiple FAST cache LUNs?
    • No limited to 2 TB really depends on how much DRAM capacity you want to consume with the memory map
    • Limited to a single FAST cache LUN

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