IBM DS4700 manual Cache memory, Cache Active LEDs Description of Figure

Attention: There are different replacement FRU part numbers for the DS4700 Express controller with certain cache sizes. The DS4700 Express Storage Subsystem profile has the information on the installed cache memory size in the DS4700 Express controllers. Refer to the storage subsystem profile and see “Parts listing” on page 188 for the correct FRU part number for the DS4700 Express controller.

Cache memory

Cache memory is memory on the RAID controller that is used for intermediate storage of read and write data on the DS4700 Express 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:

vThe cache memory from either controller A or controller B has failed.

vThe cache sizes in controller A and controller B are not the same.

vThe battery has 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 DS4000 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.

1

ds470032

1

Figure 103. Cache Active LEDs

Table 47. Description of Figure 103

Number

1

Description

Cache Active LED

Chapter 4. Operating the storage subsystem 141