Re: Bad iostat numbers

Alex Turner wrote:
> The problem I see with software raid is the issue of a battery backed
> unit: If the computer loses power, then the 'cache' which is held in
> system memory, goes away, and fubars your RAID.

I'm not sure I see the difference. If data are cached, they're not written whether it is software or hardware RAID. I guess if you're writing RAID 1, the N disks could be out of sync, but the system can synchronize them once the array is restored, so that's no different than a single disk or a hardware RAID. If you're writing RAID 5, then the blocks are inherently error detecting/correcting, so you're still OK if a partial write occurs, right?

I'm not familiar with the inner details of software RAID, but the only circumstance I can see where things would get corrupted is if the RAID driver writes a LOT of blocks to one disk of the array before synchronizing the others, but my guess (and it's just a guess) is that the writes to the N disks are tightly coupled.

If I'm wrong about this, I'd like to know, because I'm using software RAID 1 and 1+0, and I'm pretty happy with it.

Craig