In a nutshell FAST Cache provides an immediate performance benefit to the busiest workloads across an entire CX4 or EMC Unified Storage System by holding a large percentage of the most frequently used data in high performance FLASH drives.
When we look at Unified Storage today you have DRAM, located close to the CPU providing nanosecond response times, acting as a lightning fast buffer in front of much slower responding disk drives. Gigabytes of DRAM can be cost prohibitive. FLASH Drives on the other hand providing millisecond response times are significantly less expensive meaning that Terrabyte FAST Cache capacities are easily achievable and while located further away from the CPU FLASH drives are large enough to cache a huge amount of hot data from many different workloads running on the system.
With FAST Cache you insert FLASH Drives into standard Disk Array Enclosure drive slots (if you don't have them installed already) and from Unisphere you mark the devices as being FAST Cache.
That's as involved as the configuration gets.
Once enabled FAST Cache monitors incoming I/O for access frequency and if the addressed data meets the criteria for promotion into FAST Cache it is copied from the back end drives into FAST Cache. While promoted the data continues to serve host reads and writes and if written to while promoted data is asynchronously copied to the back end drives. Should the promoted data need to be discarded to make room for new data a least recently used algorithm identifies what data is available to be discarded.
FAST Cache isn't dependent on the Pool storage provisioning model, non-Pool LUNs, replication operations and other functions using cache benefiting from the availability FAST Cache and since FAST Cache is available only to highly used data it's a highly efficient way of adding FLASH to a system.
You can still dedicated LUNs on a FLASH Raid Group or include FLASH as a Tier in a Pool LUN but from FLARE 30 onwards with FAST Cache I think the hottest data will occupy the cache while warm and cold data move up and down between FC and SATA tiers in FAST pools.
You have been reading FAST Cache for EMC Unified Storage by Storagezilla.
You may also wish to read The Clariion Storage Pool and Storage Services For Clariion Pool LUNs.
