Learn About Cache Memory Protection

Logical Drive Cache Settings to Protect Cache Memory

can increase I/O performance, but it requires a battery backup. Use to protect data during a failure or a failure. When you enable write cache mirroring, cached data is mirrored across two redundant controllers with the same cache size. Data left in the cache is protected by an onboard cache battery. The data written to the cache memory of one controller is also written to the cache memory of the other controller. Therefore, if one controller fails, the other can complete all outstanding write operations.

Enable the Write cache mirroring parameter for each by selecting Logical Drive >> Change >> Cache Settings .

Sometimes write caching is disabled when the batteries are low or discharged. If you enable the Write caching without batteries parameter on a logical drive, write caching continues even when the batteries in the controller module are discharged. If you do not have an uninterruptible power supply (UPS) for power protection, or if you do not have controller batteries, do not enable this parameter. Data in the cache is lost during a power outage when the controller module does not have working batteries.

Storage Subsystem Cache Settings to Protect Cache Memory

To prevent data loss or corruption, the controller periodically writes, or flushes, cache data to the disk. When the amount of unwritten data in the cache reaches a certain level, called a start percentage, the storage management software signals the controller to write the data to disk. The controller writes to disk until the amount of data in cache drops to a stop percentage level. For example, you can specify that the controller start flushing the cache when the cache reaches 80 percent full and stop flushing the cache when the cache reaches 16 percent full.

For maximum data protection, you can choose low start percentages and stop percentages. However, in both cases, this choice increases the chance that data needed for a read will not be in the cache, which decreases performance. Choosing low start percentages and low stop percentages also increases the number of disk writes necessary to maintain the cache level, which increases system overhead and further decreases performance.

If a power outage occurs, data in the cache that has not been written to the disk drive media will be lost, even if it is mirrored to the cache memory of both controllers. For protection against this occurrence, batteries in the controller module protect against power outages. Change the controller module batteries at the recommended time intervals. The storage management software features a battery age clock that you can set when you replace a battery. This clock keeps track of the age (in days) of the battery, so you know when it is time to replace the battery. When the battery is nearing expiration and when it has reached expiration, you receive critical alert notifications.

Related Links: