![background image](http://html.mh-extra.com/html/ibm/totalstorage-ds5100/totalstorage-ds5100_installation-users-and-maintenance-manual_609021196.webp)
Attention:
There are different replacement FRU part numbers for the controller
with certain cache sizes. The storage subsystem profile has the information on the
installed cache memory size in the controllers. Refer to the storage subsystem
profile and see “Parts list” on page 208 for the correct FRU part number for the
controller.
Cache memory
Cache memory
is memory on the RAID controller that is used for intermediate
storage of read and write data on the DS5100 and DS5300 RAID controllers. Using
cache memory can increase system performance. The data for a read operation
from the host might be in the cache memory from a previous operation (thus
eliminating the need to access the drive itself), and a write operation is completed
when it is written to the cache, rather than to the drives.
The RAID controller has a Cache Active LED that displays the current status of the
cache. The LED is on if there is data in the cache, and it is off if there is no data in
the cache.
If caching is enabled and the Cache Active LED never comes on during I/O activity,
it indicates one of the following conditions:
v
The cache memory from either controller A or controller B failed.
v
The cache sizes in controller A and controller B are not the same.
v
The battery failed. (In this case, one or both of the green Battery LEDs will be off
and one or both amber Battery Needs Attention LEDs will be lit.)
Note:
Always use the DS Storage Manager client to check your cache memory
settings before assuming a hardware failure.
Figure 103 shows the locations of the Cache Active LEDs on the front of the RAID
controllers.
Subsystem cache battery
The DS5100 and DS5300 interconnect-battery unit contains two battery packs that
provide backup power to maintain any cached data not written to disks in the event
of a power loss. The battery packs can provide power to the data caches in the
RAID controllers for up to thirty minutes for the controllers to flush cache memory to
flash memory modules in the event of power loss.
Controller A
ds50010
Controller B
Cache active LED
Cache active LED
Figure 103. Cache Active LEDs
164
IBM System Storage DS5100 and DS5300 Storage Subsystem: Installation, User’s, and Maintenance Guide