linux-kernel - Re: [dm-devel] [PATCH 0/3] add resync speed control for dm-raid1

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Message-ID: <20121211085645.GH32224@suse.de>
Date:	Tue, 11 Dec 2012 09:56:45 +0100
From:	Lars Marowsky-Bree <lmb@...e.de>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	gzhao@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [PATCH 0/3] add resync speed control for dm-raid1

On 2012-12-10T13:21:23, NeilBrown <neilb@...e.de> wrote:

> The problem with this approach is that it slows down resync even when there
> is no other IO happening.
> If that is deemed to be acceptable, then the patch set seems fine, though I
> would probably make the default a lot higher so as not to change current
> default behaviour for anyone.

I agree to the latter part.

The difficulty is that our primary use case here is preventing IO
starvation while cluster raid is resyncing; and we don't know the IO
load on other nodes, or what other LVs might inflict on the same backend
store / PV. Hence, a static limit probably is the easiest way to
start.

I agree that a more dynamic approach would be desirable, but that
appears to be very complex to get right.

Thanks,
    Lars

-- 
Architect Storage/HA
SUSE LINUX Products GmbH, GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB 21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde

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