• 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