Re: Software RAID5 with 2.6.0-test

[bill davidsen]

In article <20031017192419.GG8711@xxxxxxxxxxxxx>,
Jakob Oestergaard  <jakob@xxxxxxxxxxxxx> wrote:

| Now that I'm posting anyway - I thought of a plus for the HW RAID
| controllers (hey, they're way behind on the scoreboard so far, so I
| might as well be a gentleman and give them a point or two):
| *) Battery backed write cache
| 
| This will allow the controller to say 'ok I'm done with your sync()',
| way before the data actually reaches the disk platters.  For some
| workloads this can be a big win.

Unless the drives are battery backed up as well, I'm not sure that this
is a good thing, or at least a safe thing. And if a write error happens
after the controller tells you the sync() is done? That's a question,
not a comment, I'm not sure Linux software RAID would relocate if the
drive was out of spare sectors, either, but it at least could.

I don't question your statement that caching helps performance, but I
think there is some loss of reliability. I have no numbers to estimate
the effect, so take it as a comment only.
-- 
bill davidsen <davidsen@xxxxxxx>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.
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