HP 2000i HP StorageWorks 2000i G2 Modular Smart Array user guide (481598-002, - Page 19

MSA2000 3.5\, MSA70 2.5” 25-drive enclosure, Cache, Transportable CompactFlash

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MSA2000 3.5" 12-drive enclosure 1 23 45 0 0 12 6 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 MSA70 2.5" 25-drive enclosure The 2324i G2 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 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. Transportable CompactFlash During a power loss or array controller failure, data stored in cache are saved off to non-volatile memory (CompactFlash). These data are 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 on page 52 for more information.) Controller Module CompactFlash HP StorageWorks 2000i G2 Modular Smart Array User Guide 19

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HP StorageWorks 2000i G2 Modular Smart Array User Guide
19
MSA2000 3.5" 12-drive enclosure
MSA70 2.5” 25-drive enclosure
The 2324iG2 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 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.
Transportable CompactFlash
During a power loss or array controller failure, data stored in cache are saved off to non-volatile memory
(CompactFlash). These data are 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
on page 52 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
2
6
1
2
CompactFlash
Controller Module