CLARiiON Fast Cache

Temporarily relocates often-used data to faster storage resources


  • Closest to CPU, front-end, highest speed possible
  • Smallest page size – 2KB-16KB
  • Granularity is IO size
  • Limited size (GBs)

FAST Cache

  • One step further
  • 64KB extents
  • Significantly large size (TBs)

Current Architecture

  1. DRAM @ 10^-9
  2. FC Drives 10^-3

New Architecture

  1. DRAM 10^-9
  2. FLASH Cache 10^-6
  3. FC Drives 10^-3

Release 30

  • Dedicated set of standard EFD drives
  • Native mirrored RAID protection
  • Code runs on SP CPU/memory
  • Installation
    • Non-disruptive
    • Add or allocate flash drives
    • NDU FAST Cache enabler
    • GUI or CLI management
  • Flash drive deployment recommendation
    • FAST Cache
    • FAST (tiering)
    • Dedicated drives


  • Memory based map tracks host address usage and ownership at 64KB extents
  • Dedicated LUNs in dedicated Flash drive pool
  • Chunks of data copied as needed
    • Heavily used data temporarily moves to flash from home HDD LUNs
    • Moves back home when other data becomes more heavily used

Clariion Stack

  • Backend
  • RAID
  • SP Cache
  • FAST Cache Drive (Cache Policy Engine + Memory Map)
  • Replication/Virtualization
  • Host-side front-end

IO Request

  1. IO request is received by cache driver
  2. Memory map is searched, no match found
  3. IO is directed at target HDD LUN
  4. IO performance same as without flash
  5. Asynchronous copy from HDD to EFD
  6. Later if a write goes to the EFD, the map will be marked dirty to indicate that the live copy of data only exists in EFD and later needs to be copied back to HDD
  7. Note: there is no forced flushing, copy process will no proceed until space is available

Performance Benefits

  • FAST Cache read hits = Flash drive response times
  • FAST Cache write hits flush faster
  • FAST Cache hits offload HDDs
  • Lower net application response time enables higher IOPS
  • Efficient use of Flash drive capacity

Evaluating Workloads

  • Small to moderate work set size where most request go to a subset of allocated space
  • High frequency of access to the same chunks, re-hit
  • Performance currently limited by disk capability, not SP capability
  • Profiles
    • Database OLTP, DSS (Oracle, SQL)
    • Exchange
    • File serving
  • Determine appropriate subset of LUNs
    • Default – FAST Cache enabled for all eligible LUNs
    • LUN performance grade for FAST Cache
    • Enable FAST Cache for performance-critical LUNs first
      • FAST LUN Migrator can help identify them
    • FAST Cache not effective for some LUNs
      • Sequential workloads (DRAM cache with HDD)
      • Wide spread random workloads (few extent re-hits)
  • In their testing, they were able to achieve the same performance on the following configurations:
    • 300x FC drives, 1/4 stroked with no FAST Cache
    • 100x FC drives, 1/2 stroked with 2TB FAST Cache (savings of 200x FC drives)
    • Very impressive


  • FAST Cache capacity from 73GB to 2TB available
  • Usage modes
    • R/W – mirrored protection (R1)
    • Read-only – individual drive option (lower cost per GB)
  • Drive placement
    • Same as any EFD deployment
    • Dedicated DAEs and buses not required
  • Can be applied to any HDD LUN
    • Standard RAID group LUN, metaLUN, pool-based LUN
    • Enabled/disable at RG LUN or at pool level
  • DRAM space re-allocated to FAST Cache maps
  • Drive choices
    • 73GB: best for write intensive loads
    • 200GB: good all-around usage
    • Spread load for best performance
    • Account for hot spares
  • Configured under Storage System Properties > FAST Cache
  • Also configured at LUN level, Create LUN > Advanced > check off FAST Cache


  • Pre-deployment locality profiling
    • FAST Cache Analyzer (internal and/or service) – TBD
  • Navisphere Analyzer
    • SP level statistics (FAST Cache dirty pages, MB/s flushed)
    • LUN level FAST Cache statistics (hits and hit ratios, read/write)

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