Cache; Transportable Compactflash - HP MSA 1050 User Manual

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Cache

To enable faster data access from disk storage, the following types of caching are performed:

•

Write-back caching. The controller writes user data in the cache memory on the module rather than directly to the

drives. Later, when the storage system is either idle or aging—and continuing to receive new I/O data—the controller

writes the data to the drive array.

•

Read-ahead caching. The controller detects sequential array access, reads ahead into the next sequence of data, and

stores the data in the read-ahead cache. Then, if the next read access is for cached data, the controller immediately

loads the data into the system memory, avoiding the latency of a disk access.

NOTE: See the SMU Reference Guide for more information about volume cache options.

During a power loss or array controller failure, data stored in cache is saved off to non-volatile memory (CompactFlash).

The data is then written to disk after the issue is corrected. To protect against writing incomplete data to disk, the image

stored on the CompactFlash is verified before committing to disk.

The CompactFlash memory card is located at the midplane-facing end of the controller module as shown below.

Controller module pictorial

(Midplane-facing rear view)

Figure 9 MSA 1050 CompactFlash memory card

If one controller fails, then later another controller fails or does not start, and the Cache Status LED is on or blinking, the

CompactFlash will need to be transported to a replacement controller to recover data not flushed to disk (see

failure" (page 45)

CompactFlash memory card

for more information).

"Controller

Cache

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