linux-kernel - Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

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Message-ID: <20070613145442.GC28279@think.oraclecorp.com>
Date:	Wed, 13 Jun 2007 10:54:42 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	John Stoffel <john@...ffel.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

On Wed, Jun 13, 2007 at 10:00:56AM -0400, John Stoffel wrote:
> >>>>> "Chris" == Chris Mason <chris.mason@...cle.com> writes:
> >> As a user of Netapps, having quotas (if only for reporting purposes)
> >> and some way to migrate non-used files to slower/cheaper storage would
> >> be great.
> 
> Chris> So far, I'm not planning quotas beyond the subvolume level.
> 
> So let me get this straight.  Are you saying that quotas would only be
> on the volume level, and for the initial level of sub-volumes below
> that level?  Or would *all* sub-volumes have quota support?  And does
> that include snapshots as well?

On disk, snapshots and subvolumes are identical...the only difference is
their starting state (sorry, it's confusing, and it doesn't help that I
interchange the terms when describing features).

Every subvolume will have a quota on the number of blocks it can
consume.  I haven't yet decided on the best way to account for blocks
that are actually shared between snapshots, but it'll be in there
somehow.  So if you wanted to make a snapshot readonly, you just set the
quota to 1 block.

But, I'm not planning on adding a way to say user X in subvolume Y has
quota Z.  I'll just be: this subvolume can't get bigger than a given
size.  (at least for version 1.0).

-chris

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