Re: EVMS or md?

[hpa@zytor.com (H. Peter Anvin)]

Followup to:  <200504041446.50337.kewley@gps.caltech.edu>
By author:    David Kewley <kewley@gps.caltech.edu>
In newsgroup: linux.dev.raid
>
> Mike Tran wrote on Monday 04 April 2005 12:28:
> > We (EVMS team) intended to support RAID6 last year.  But as we all
> > remember RAID6 was not stable then.  I may write a plugin to support
> > RAID6 soon.
> 
> Hi Mike,
> 
> In your view, is RAID6 now considered stable?  How soon might you have an evms 
> plugin for it? ;)  I'd love to use evms on my new filserver if it supported 
> RAID6.
> 

I can't speak for the EVMS people, but I got to stress-test my RAID6
test system some this weekend; after having run in 1-disk degraded
mode for several months (thus showing that the big bad "degraded
write" bug has been thoroughly fixed) I changed the motherboard, and
the kernel didn't support one of the controllers.  And now there were
2 missing drives.  Due to some bootloader problems, I ended up
yo-yoing between the two kernels a bit more than I intended to, and
went through quite a few RAID disk losses and rebuilds as a result.

No hiccups, data losses, or missing functionality.  At the end of the
whole ordeal, the filesystem (1 TB, 50% full) was still quite prisine,
and fsck confirmed this.  I was quite pleased :)

Oh, and doing the N-2 -> N-1 rebuild is slow (obviously), but not
outrageously so.  It rebuilt the 1 TB array in a matter of
single-digit hours.  CPU utilitization was quite high, obviously, but
it didn't cripple the system by any means.

	-hpa