HP StorageWorks 2000fc G2 Modular Smart Array - Manual (Page 19)

HP 2312fc and 2324fc Modular Smart Array user guide 19
MSA2000 3.5 12-drive enclosure
NOTE: The MSA2324fc can also be attached to an MSA70 that is running firmware version 2.18 or later.
For information about the MSA70, see the HP StorageWorks 70 Modular Smart Array Enclosure user guide
located on the MSA2000 Software Support/Documentation CD shipped with your product or at
http://hp.com/support/manuals .
Cache
To enable faster data access from disk storage, the following two types of caching are performed:
• Posted-write 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 idle, 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.
Transportable CompactFlash
During a power loss or array controller failure, data stored in cache is saved off to non-volatile memory
(CompactFlash). This 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.
In single-controller configurations, if the controller has failed 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 Controller failure in a single-controller configuration for more information.)
1 Power supplies
2 Power switches
3 SAS In port (connects to a controller enclosure)
4 Service port (used by service personnel only)
5 SAS Out port (connects to another drive enclosure)
6 Optional I/O module
1 3 4 5 1 2 2 6
CompactFlash