Resolving NVRAM problems

NVRAM battery failure

If the NetCache appliance detects low batteries on the NVRAM card, it gives advance warning and automatically shuts down every 24 hours.

If the NetCache appliance is in RAID degraded mode and the NVRAM batteries are low, it fails to boot. You must replace the NVRAM batteries immediately.

NVRAM battery failures generally do not cause data loss. When the NetCache appliance executes the halt command, it flushes the contents of NVRAM to disk, then turns off the NVRAM so that no battery power is used.

Inconsistent NVRAM contents

This kind of data error can occur only when you boot a system after a failure or after you turn off a NetCache appliance without using the halt command.

The NetCache appliance performs a number of checks to ensure that the NVRAM contents are consistent. If the contents are inconsistent, it discards the inconsistent contents and dumps core.

The file requests received during the last few seconds before the NetCache appliance shuts down are lost. This does not cause the file system to become inconsistent, but files written during the last 10 seconds before shutdown might contain old or incorrect data. Also, because the parity of some recently written stripes might be incorrect, the NetCache appliance must perform a parity check on the entire RAID array. The parity check (and any correction) is performed online, in the background, while continuing otherwise normal operation.