Would the data on the RAID Card Cache and Drive Cache be lost when a kernel panic happens

cachedisk-cachehardware-raidkernel-panicraid

Is a BBU necessary when you have A+B power?

Would the data on the RAID Card Cache and Drive Cache be lost when a kernel panic happens and you are forced to do a cold reset?

Best Answer

Some of this has been covered here before... and here, too. I can't think of any situation where you wouldn't want a battery-backed or flash-backed cache unit on your hardware RAID controller. It's what makes write caching possible.

See: BBWC: in theory a good idea but has one ever saved your data?

If your system panics suddenly, the question as to what happens to in-flight disk transitions depends a bit on the nature of the crash, when it happens, the filesystem in use and your storage subsystem. I've had data corruption in some cases and I've also had the RAID controller cache save the day.

Cache Status Details: The current array controller had valid data stored in its battery/capacitor backed write cache the last time it was reset or was powered up. This indicates that the system may not have been shut down gracefully. The array controller has automatically written, or has attempted to write, this data to the drives. This message will continue to be displayed until the next reset or power-cycle of the array controller.

With regard to A/B power feeds, it's nice that your datacenter or facility provide it, but it should have no bearing on your RAID controller caching decision.

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