[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]
Re: swap-on-raidframe vs raidctl -P
der Mouse writes:
> I've just set up a 4.0 machine at work. It's using raidframe for
> everything (well, not quite; there's a tiny boot partition that's not
> formally raided, though it is mirrored another way), and I saw a
> Swap is on raid0b, and, when raidframeparity ran, it complained that
> raid0 parity was dirty and started a parity rewrite.
in /etc/rc.conf , yes? That should take care of most instances of
this rewrite problem...
> This is hardly a
> catastrophe; the rewrite finishes fast enough that it's not a huge
> problem. But it seems to me that this is suboptimal.
> I see two possible fixes.
> One would be a way to configure raidframe for uses (like swap) that
> don't care about data preservation when the partition is not in use;
> parity rewrite at boot would be dummied out for such partitions.
This might work for RAID 1, but it will *not* work for RAID 5.
Consider a RAID 5 set, used for swap, where there is a stripe with
bad parity. Let the blocks of that stripe be A, B, and P. A "small
write" to A will read P, compute P', and write out A' and P'. Now
consider that the disk containing A' dies. B and P' will now be used
to compute A'. Unfortunately, P was not in sync with A and B
initially, so B and P' cannot be used to compute the correct value of
A'. You end up swapping in 'garbage', and your system dies.
> at boot; if a member fails and is replaced, the resulting rewrite
> should not be dummied out, at least not for blocks that have been
> written since boot - and keeping track of which blocks that is would be
> expensive enough that I'd be inclined to say it shouldn't be done.)
> The other would be to run raidframeparity earlier, before swap is
I'm not sure what this would fix... whether or not swap is started on
a partition matters not a wit to RAIDframe in determining whether a
partition is in need of a parity check or not -- what matters is whether
or not raidclose() got called on the last open partition on a RAID
set at the last shutdown...
> It seems to me that each should actually be done, independent of the
> other, but either one would be good enough for my purposes. The former
> would be more intrusive as far as raidframe is concerned; I'm not sure
> the latter is possible, since I don't have my head around why it's run
> where it is now (rather than as part of raidframe).
> /~\ The ASCII der Mouse
> \ / Ribbon Campaign
> X Against HTML mouse%rodents.montreal.qc.ca@localhost
> / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
Main Index |
Thread Index |