From: Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>
To: Paul Clements <paul.clements@us.sios.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: bitmap questions
Date: Thu, 14 Oct 2010 08:00:38 +0200 [thread overview]
Message-ID: <201010140800.38419.a.miskiewicz@gmail.com> (raw)
In-Reply-To: <AANLkTikBAi=NO-uzkvtzwYsgLSf44KuA1VmvXj3d708_@mail.gmail.com>
On Thursday 14 of October 2010, Paul Clements wrote:
> On Wed, Oct 13, 2010 at 12:24 PM, Arkadiusz Miskiewicz
>
> <a.miskiewicz@gmail.com> wrote:
> > I have a question on how bitmap works and what's shown in /proc/mdstat,
> > for example:
> >
> > md2 : active raid10 sdc3[0] sdd3[3] sdb3[2] sda3[1]
> > 60002560 blocks 64K chunks 2 near-copies [4/4] [UUUU]
> > bitmap: 1/1 pages [4KB], 65536KB chunk
> >
> > - 1 bitmap for 4096 chunks
> >
> > - if it shows 0/1 pages [0KB] what does it actually mean?
>
> If it's 0 pages then no resync.
> I assume you mean 1/1 ?
Ok, I thought differently since it's bitmap->pages - bitmap->missing_pages
(thought that missing_pages == dirty one).
> > Does that mean that
> > in case of resync it will resync _all_ 4096 chunks in that page or only
> > chunks that require that (for example 7 chunks) ?
>
> It only resyncs what is dirty. A page dirty in the in-memory bitmap
> does not mean ALL bits are dirty, just that the page is allocated.
So there is no way to know in advance how much is going to be resynced when
sudden reset would happen in that moment?
Anyway good to know that 1 page setup also makes sense :)
> --
> Paul
--
Arkadiusz Miśkiewicz PLD/Linux Team
arekm / maven.pl http://ftp.pld-linux.org/
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next prev parent reply other threads:[~2010-10-14 6:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-13 16:24 bitmap questions Arkadiusz Miskiewicz
2010-10-14 5:02 ` Paul Clements
2010-10-14 6:00 ` Arkadiusz Miskiewicz [this message]
2010-10-14 12:11 ` John Robinson
2010-10-14 12:39 ` Mario 'BitKoenig' Holbe
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