linux-kernel - Re: Out-of-order writing by disk drives

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Message-Id: <E1Ltla2-0000bS-5j@a4.complang.tuwien.ac.at>
Date:	Tue, 14 Apr 2009 18:33:50 +0200 (CEST)
From:	"Anton Ertl" <anton@...s.complang.tuwien.ac.at>
To:	andi@...stfloor.org (Andi Kleen)
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Out-of-order writing by disk drives

Andi Kleen wrote:
> 
> "Anton Ertl" <anton@...s.complang.tuwien.ac.at> writes:
> >
> > /dev/md2        /home           ext3    defaults,barrier=1      1	2
> 
> Just make sure /dev/md2 is a RAID1, MD RAID0/5/10 don't support barriers.

Thank you.  I added the following to the README:

|Note that, as of this writing (2009-04), not all Linux devices support
|barriers, in particular md devices only support them in RAID 1 mode;
|the kernel will reportedly warn about the lack of barriers if you try
|to use ext3 with barriers on a device that does not support barriers
|(look in, e.g., dmesg).

> See also my general treatise of multiple device barriers earlier today.

I guess you mean <878wm3903h.fsf@...il.nowhere.org> in the
"dm-multipath and write request ordering" thread.  Thank you for the
pointer.

- anton

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