From: Jakob Oestergaard <jakob@unthought.net>
To: Anders Karlsson <anders@trudheim.com>
Cc: Riley Williams <Riley@Williams.Name>,
Clemens Schwaighofer <cs@tequila.co.jp>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: Two RAID1 mirrors are faster than three
Date: Mon, 19 May 2003 10:19:14 +0200 [thread overview]
Message-ID: <20030519081914.GB14971@unthought.net> (raw)
In-Reply-To: <1052995874.3248.20.camel@tor.trudheim.com>
On Thu, May 15, 2003 at 11:51:14AM +0100, Anders Karlsson wrote:
...
> No, it should not cause problems as when you add the split-off copy back
> into the mirror, it is treated as 'stale' and will get synchronised with
> the original.
Correct
If this was not the case, background resynchronization of standard
2-disk RAID-1 would be a really horrible feature (with half the reads
returning stale data from the new disk)...
>
> I would be very surprised if the Linux software md driver worked any
> diffrently than this. Perhaps someone that knows it in-depth can add to
> the conversation?
Unless there's bugs in the driver, your description is correct :)
>
> With the facilities of LVM 'snapshots' now being available, this
> practice of splitting off one copy from a three-way mirror is perhaps
> becoming redundant, but people will likely take the approach of "if it
> ain't broken, don't fix it" and leave old backup methods as they are.
> So if you work in the sysadm field, you might well come across this
> practice.
The really good argument for N>2 disk RAID-1 is still the seek-time and
multiple-readers performance benefits which you won't be addressing with
LVM snapshots.
--
................................................................
: jakob@unthought.net : And I see the elder races, :
:.........................: putrid forms of man :
: Jakob Østergaard : See him rise and claim the earth, :
: OZ9ABN : his downfall is at hand. :
:.........................:............{Konkhra}...............:
next prev parent reply other threads:[~2003-05-19 8:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-12 2:10 Two RAID1 mirrors are faster than three Chuck Ebbert
2003-05-12 4:35 ` Clemens Schwaighofer
2003-05-12 5:10 ` Anders Karlsson
2003-05-12 5:41 ` Paul P Komkoff Jr
2003-05-12 7:23 ` Anders Karlsson
2003-05-12 8:40 ` Clemens Schwaighofer
2003-05-12 9:30 ` [OT] " Anders Karlsson
2003-05-12 11:20 ` Paul P Komkoff Jr
2003-05-12 14:29 ` Valdis.Kletnieks
2003-05-13 2:24 ` Clemens Schwaighofer
2003-05-13 7:41 ` Anders Karlsson
2003-05-12 14:56 ` Lars Marowsky-Bree
2003-05-15 7:21 ` Riley Williams
2003-05-15 10:51 ` Anders Karlsson
2003-05-19 8:19 ` Jakob Oestergaard [this message]
2003-05-12 16:32 Chuck Ebbert
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