Hitachi G1500 - Cache Flash Memory

Cache flash memory
The cache ash memory (CFM) is contained in the cache backup modules in the
contr
oller, along with the cache backup batteries. Similar to the cache memory, a CFM
featur
e consists of a pair for r
edundancy purposes. The CFM backup the cache in case of
po
wer or component failure. The following gure shows two CPAs (2-3 and 1-4).
Cache flash memory operation
Each CFM blade connects directly to its corresponding CPA blade and backs up the data
in that CP
A blade if power fails. When data that is not stored on disk is written to the
cache, it is written to one blade of the CPA and mirrored to the other. If one CFM fails, or
one phase of the power fails, the other CFM backs up the mirrored data from its
corresponding CPA blade, and no data is lost. In the unlikely event where a CFM has
failed and a full power failure occurs, the other CFM backs up the mirrored data from the
CPA without any loss of data.
Cache flash memory capacity
The recommended size of the installed cache ash memory depends on the size of the
cache memory
, and is automatically selected when dening the conguration for the
system.
The following table sho
ws CFM capacities per contr
oller with both small and lar
ge cache
memory backup assemblies.
Number of
controllers
Number of CFM
features (pairs of
boxes)
Memory module
size CFM size
1
1 1 CFM
2 boxes / SSDs
128 GB 256 GB
256 GB 512 GB
2 CFMs
4 box
es / SSDs
128 GB 512 GB
256 GB 1 TB
2 1 CFM
2 boxes / SSDs
128 GB 512 GB
256 GB 1 TB
Cache ash memory
Chapter 2: Storage system hardware overview
Hitachi Virtual Storage Platform G1000, G1500, and VSP F1500 Hardware Guide 58