From: Neil Brown <neilb@suse.de>
To: Asdo <asdo@shiftmail.org>
Cc: linux-raid@vger.kernel.org
Subject: Re: Why does one get mismatches?
Date: Wed, 3 Mar 2010 07:17:01 +1100 [thread overview]
Message-ID: <20100303071701.040f2a51@notabene.brown> (raw)
In-Reply-To: <4B8D5581.8070509@shiftmail.org>
On Tue, 02 Mar 2010 19:14:25 +0100
Asdo <asdo@shiftmail.org> wrote:
> Luca Berra wrote:
> >>>
> >>> I will try to explain better,
> >>> the problem is not related to the confusion between B or B'
> >>>
> >>> the problem is that on one disk we have B' _without_ C.
> >>>
> >> You're demanding full atomic commits; this is precisely what journals
> >> and /barriers/ are for.
> >>
> >> Are you are bypassing them in a quest for performance and paying for
> >> it on crashes?
> >> Or is this a hardware bug?
> >> Or is it some glitch in the block device layering leading to barrier
> >> requests not being honored?
> > I just asked for confirmation that with /barriers/ the scenario above
> > would not happen.
> >
>
> I think so, that it would not happen: the filesystem would stay
> consistent. (while the mismatches could still happen)
>
> The problem is that the barriers were introduced in all md raids in the
> 2.6.33 (just released), and also I have read XFS has a major performance
> drop with barriers activated. People will be tempted to disable
> barriers. AFAIR the performance drop was visible with 1 disk alone,
> imagine now with RAID. And I expect similar performance drops with other
> filesystems, correct me if I am wrong.
The barrier support added in 2.6.33 was for striped md arrays.
RAID1, which is not striped, has had barrier support since about 2.6.16,
as it is much easier to implement.
NeilBrown
>
> Now it would be interesting to understand why the mismatches don't
> happen when LVM is above MD-raid!?
> The mechanisms presented up to now on this ML for mismatches don't
> explain why on LVM the same issue doesn't show up. I think.
> So you might want to use raid-1 and raid-10 under LVM, just in case....
> --
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next prev parent reply other threads:[~2010-03-02 20:17 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-20 11:52 Fw: Why does one get mismatches? Jon Hardcastle
2010-01-22 18:13 ` Goswin von Brederlow
2010-01-24 17:40 ` Jon Hardcastle
2010-01-24 21:52 ` Roger Heflin
2010-01-24 23:13 ` Goswin von Brederlow
2010-01-25 10:07 ` Jon Hardcastle
2010-01-25 10:37 ` Goswin von Brederlow
2010-01-25 10:52 ` Jon Hardcastle
2010-01-25 17:32 ` Goswin von Brederlow
2010-01-25 19:32 ` Iustin Pop
2010-02-01 21:18 ` Bill Davidsen
2010-02-01 22:37 ` Neil Brown
2010-02-02 15:11 ` Bill Davidsen
2010-02-03 11:17 ` Goswin von Brederlow
2010-02-11 5:14 ` Neil Brown
2010-02-11 17:51 ` Bryan Mesich
2010-02-16 21:25 ` Bill Davidsen
2010-02-16 21:38 ` Steven Haigh
2010-02-17 3:19 ` Bryan Mesich
2010-02-17 23:05 ` Neil Brown
2010-02-19 15:18 ` Piergiorgio Sartor
2010-02-19 22:02 ` Neil Brown
2010-02-19 22:37 ` Piergiorgio Sartor
2010-02-19 23:34 ` Asdo
2010-02-20 4:27 ` Goswin von Brederlow
2010-02-20 11:12 ` Asdo
2010-02-21 11:13 ` Goswin von Brederlow
[not found] ` <8754A21825504719B463AD9809E54349@m5>
[not found] ` <20100221194400.GA2570@lazy.lzy>
2010-02-22 13:01 ` Asdo
2010-02-22 13:30 ` Piergiorgio Sartor
2010-02-22 13:44 ` Piergiorgio Sartor
2010-02-24 19:42 ` Bill Davidsen
2010-02-20 4:23 ` Goswin von Brederlow
2010-02-24 14:54 ` Bill Davidsen
2010-02-24 21:37 ` Neil Brown
2010-02-26 20:48 ` Bill Davidsen
2010-02-26 21:09 ` Neil Brown
2010-02-26 22:01 ` Piergiorgio Sartor
2010-02-26 22:15 ` Bill Davidsen
2010-02-26 22:21 ` Piergiorgio Sartor
2010-02-26 22:20 ` Asdo
2010-02-27 6:01 ` Michael Evans
2010-02-28 0:01 ` Bill Davidsen
2010-02-24 14:46 ` Bill Davidsen
2010-02-24 16:12 ` Martin K. Petersen
2010-02-24 18:51 ` Piergiorgio Sartor
2010-02-24 22:21 ` Neil Brown
2010-02-25 8:41 ` Piergiorgio Sartor
2010-03-02 4:57 ` Neil Brown
2010-03-02 18:49 ` Piergiorgio Sartor
2010-02-24 21:39 ` Neil Brown
[not found] ` <4B8640A2.4060307@shiftmail.org>
2010-02-25 10:41 ` Neil Brown
2010-02-28 8:09 ` Luca Berra
2010-03-02 5:01 ` Neil Brown
2010-03-02 7:36 ` Luca Berra
2010-03-02 10:04 ` Michael Evans
2010-03-02 11:02 ` Luca Berra
2010-03-02 12:13 ` Michael Evans
2010-03-02 18:14 ` Asdo
2010-03-02 18:52 ` Piergiorgio Sartor
2010-03-02 23:27 ` Asdo
2010-03-03 9:13 ` Piergiorgio Sartor
2010-03-03 11:42 ` Asdo
2010-03-03 12:03 ` Piergiorgio Sartor
2010-03-02 20:17 ` Neil Brown [this message]
2010-02-24 21:32 ` Neil Brown
2010-02-25 7:22 ` Goswin von Brederlow
2010-02-25 7:39 ` Neil Brown
2010-02-25 8:47 ` John Robinson
2010-02-25 9:07 ` Neil Brown
2010-02-11 18:12 ` Piergiorgio Sartor
-- strict thread matches above, loose matches on Subject: below --
2010-02-01 23:14 Jon Hardcastle
2010-01-25 20:43 greg
2010-01-25 22:49 ` Steven Haigh
2010-01-27 21:54 ` Tirumala Reddy Marri
2010-01-28 9:16 ` Jon Hardcastle
2010-01-28 10:29 ` Asdo
2010-01-28 17:20 ` Tirumala Reddy Marri
2010-01-28 18:23 ` Goswin von Brederlow
2010-01-28 19:03 ` Tirumala Reddy Marri
2010-01-28 20:24 ` Goswin von Brederlow
2010-01-29 15:37 ` Jon Hardcastle
2010-01-29 23:52 ` Goswin von Brederlow
2010-01-30 10:39 ` Jon Hardcastle
2010-02-01 21:10 ` Bill Davidsen
2010-01-20 15:03 Jon Hardcastle
2010-01-20 15:34 ` Brett Russ
2010-01-20 20:44 ` Majed B.
2010-01-20 22:25 ` Brett Russ
2010-01-20 22:30 ` Majed B.
2010-01-20 22:43 ` Brett Russ
2010-01-20 23:01 ` Christopher Chen
2010-01-21 4:17 ` Steven Haigh
2010-01-21 8:08 ` Asdo
2010-01-21 10:52 ` Steven Haigh
2010-01-21 11:48 ` Farkas Levente
2010-01-21 12:15 ` Jon Hardcastle
2010-01-19 10:04 Jon Hardcastle
2010-01-20 14:19 ` Brett Russ
2010-01-20 14:34 ` Jon Hardcastle
2010-01-20 14:46 ` Brett Russ
2010-02-01 20:48 ` Bill Davidsen
2010-01-22 16:22 ` Jon Hardcastle
2010-01-22 16:34 ` Asdo
2010-01-22 17:41 ` Brett Russ
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