Re: swap-on-raidframe vs raidctl -P

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Tue, 22 Jan 2008 10:17:20 -0500 (EST)
der Mouse <mouse%Rodents.Montreal.QC.CA@localhost> wrote:

> 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
> problem.
> 
> Swap is on raid0b, and, when raidframeparity ran, it complained that
> raid0 parity was dirty and started a parity rewrite.  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.

Without touching on your other points below, do you have swapoff=YES
in /etc/rc.conf?
> 
> 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.
> (Only 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.)

I think that this is an excellent idea.
> 
> The other would be to run raidframeparity earlier, before swap is
> started.
> 
> 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).
> 
> Comments?
> 
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                --Steve Bellovin, http://www.cs.columbia.edu/~smb