dead RAID controller battery--any impact? Does it slow Foglight Experience Viewer (FxV) system performance, for example?
Whenever you see a failed controller battery, you should check the write policy of the virtual disk. If it is set to "Write Through", the write performance has been degraded. This performance degradation may not be noticed on lightly loaded systems but will definitely reduce the capture capacity of the Archiver. The difference it makes is like night and day.
Action to take:
So the next action is to replace the RAID controller battery--especially if the write policy is set to "Write Through".
The write policy on the R710 and R720 PERC controllers can be set to either "Write Back" or "Write Through". When set to "Write Through", the controller sends a data transfer complete signal to the OS when the disk subsystem has received all the data. When set to "Write Back", the controller sends a data transfer complete signal to the OS when the controller cache has received all the data. When "Write Back" mode is enabled, the controller will flush the data out of the cache in the background. This significantly speeds up the disk write performance.
When the controller battery is dead or low on charge, this write cache is disabled since the battery is incapable of preserving the cache contents in the event of a failure. The performance impact is highly dependent on the application but, since the Archiver is always writing to the disk when traffic is present, it can significantly impact Archiver performance.
On the R710 this battery is used to preserve the cache contents until power is restored. Depending on the battery charge and size of cache, this can be roughly 48 to 72 hours. On the R720, the battery is used to keep the controller alive, momentarily, until the cache contents can be written to non-volatile memory. This non-volatile memory will preserve the cache contents forever since it does not rely on the battery.
So the next question is "how do you check the write policy of the virtual disk?" On FxV version 5.6.6, if you create a support bundle and unzip it, look in the /support/diag/omreport.txt file. This will tell you all sorts of useful information of not just the write policy but also information on the health of the disks, batteries, CPUs, and memory.
The /support/diag/ALL_DIAGS.txt file, that is contained in support bundles taken from a version FxV 5.6.6 will also tell you the write policy as well along with the other health information, but it is not as concise as the omreport.txt file. On version 5.6.5, there is no omreport.txt file generated and the ALL_DIAGS.txt doesn't contain nearly as much diagnostic information, such as the write policy.
Below is more information I found about write policy: