RAID battery-backed cache - necessary?

Adam Nielsen adam.nielsen at uq.edu.au
Wed Feb 10 19:25:17 CST 2010


> If the power fails to the system, or the kernel crashes, the OS level
> cache will never be written to disk and data may be lost.  In the
> event of a power failure, the battery backed RAID cache will be
> written to disk when power is restored. This allows processes that
> like to confirm their data has been stored to disk before moving on
> (like databases, or even journaling file system writes) to continue
> once the data has been written to the RAID cache - which completes
> significantly faster than the physical media can complete the
> operation.

Ahh, okay, so it's not there for pure write speed as such, it's there so 
that software can be told "yes, the data you just wrote is now on disk 
no matter what" even though the actual disk write may happen at a later 
time.

I guess although a UPS would stop the OS cache from going away, it can't 
help if the kernel crashes.

Well that answers my question - thanks :-)

Cheers,
Adam.



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