From: Hugo Mills <hugo@carfax.org.uk>
To: Brendan Hide <brendan@swiftspirit.co.za>
Cc: Sebastien Luttringer <sebastien.luttringer@smartjog.com>,
linux-btrfs@vger.kernel.org
Subject: Re: Feeback on RAID1 feature of Btrfs
Date: Tue, 18 Dec 2012 12:13:11 +0000 [thread overview]
Message-ID: <20121218121311.GL19051@carfax.org.uk> (raw)
In-Reply-To: <50D05174.4060109@swiftspirit.co.za>
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On Tue, Dec 18, 2012 at 01:20:20PM +0200, Brendan Hide wrote:
> On 2012/12/17 06:23 PM, Hugo Mills wrote:
> >On Mon, Dec 17, 2012 at 04:51:33PM +0100, Sebastien Luttringer wrote:
> >>Hello,
> snip
> >>I get the feeling that RAID1 only allow one disk removing. Which is more
> >>a RAID5 feature.
> > The RAID-1 support in btrfs makes exactly two copies of each item
> >of data, so you can lose at most one disk from the array safely. Lose
> >any more, and you're likely to have lost data, as you've found out.
> >>I'm afraid Btrfs raid1 will not be working before the end of the world.
> > It does work (as you demonstrated with the first disk being
> >removed) -- but just not as you thought it should. Now, you can argue
> >that "RAID-1" isn't a good name to use here, but there's no good name
> >in RAID terminology to describe what we actually have here.
> Technically, btrfs's "RAID1" implementation is much closer to RAID1E
> than traditional RAID1. See
> http://en.wikipedia.org/wiki/Non-standard_RAID_levels#RAID_1E or http://pic.dhe.ibm.com/infocenter/director/v5r2/index.jsp?topic=/serveraid_9.00/fqy0_craid1e.html
>
> Perhaps a new name, as with ZFS, might be appropriate. RAID-Z and
> RAID-Z2, for example, could not adequately be described by any
> existing RAID terminology and, technically, RAID-Z still isn't a
> RAID in the classical sense.
Yeah, we did have a naming scheme proposed, with combinations of
nCmSpP, where n is the number of copies held, m the number of stripes,
and p the number of parity stripes. So btrfs RAID-1 is 2C, RAID-5 on 5
disks would be 4S1P, and RAID-10 on 4 disks would be 2C2S. I'd prefer
to see that than some non-"standard" RAID-18KTHXBYE formulation.
Plenty of room for shed-painting here, though.
Hugo.
--
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
--- I believe that it's closely correlated with ---
the aeroswine coefficient.
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next prev parent reply other threads:[~2012-12-18 12:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-17 15:51 Feeback on RAID1 feature of Btrfs Sebastien Luttringer
2012-12-17 16:17 ` Bart Noordervliet
2012-12-17 16:23 ` Hugo Mills
2012-12-18 11:20 ` Brendan Hide
2012-12-18 12:13 ` Hugo Mills [this message]
2012-12-19 11:01 ` C Anthony Risinger
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