Array Accelerator Features; Array Accelerator Batteries - HP 201723-B21 - StorageWorks Modular SAN Array 1000 Hard Drive Reference Manual

MSA1000 Hardware Components
The read-ahead cache detects sequential accesses to the array, reads ahead data,
and stores the data in the cache until the next read access arrives. If the data is of a
sequential nature, the data can be loaded immediately into memory, avoiding the
latency of a disk access.
If the MSA1000 Controller fails before cached data is stored on the disk, the
Array Accelerator and its integrated batteries may be removed from one
MSA1000 Controller and installed on a replacement controller. Any data in the
Array Accelerator that has not been written to the hard drive will be transferred to
the replacement MSA1000 Controller.

Array Accelerator Features:

Other features of the Array Accelerator:
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Array Accelerator Batteries

The Array Accelerator has two rechargeable and replaceable Nickel Metal
Hydride (NiMH) battery packs. Under normal operating conditions, these should
last for three years before replacement is necessary. They are continuously
recharged via a "trickle" charging process whenever the MSA1000 storage system
is powered on.
The battery packs protect data on the Array Accelerator against equipment failure
or power outage for up to four continuous days.
Note:
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Mounted on a removable daughterboard (allows stored data to be moved to
another controller if the original controller fails)
Backed up with replaceable batteries
Upgradable to 512 MB (256 MB per controller)
Adjustable read/write ratio - usually set during array configuration but can be
changed at any time
16-bit Error Checking and Correcting (ECC) SDRAM memory
ECC detects and corrects all single-bit memory errors. It also detects all
two-bit memory errors in any position, and most three- and four-bit memory
errors in a single SDRAM. With ECC, an entire memory chip can also fail
without data loss. This provides a high level of data integrity by ensuring the
correction of common memory errors without affecting performance.
Temperature, age, and cache size may affect battery life.
HP StorageWorks 1000 Modular Smart Array Reference Guide