linux-kernel - Re: Btrfs: broken file system design (was Unbound(?) internal fragmentation in Btrfs)

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Date:	Wed, 23 Jun 2010 21:51:12 -0700
From:	Mike Fedyk <mfedyk@...efedyk.com>
To:	Daniel Taylor <Daniel.Taylor@....com>
Cc:	Daniel J Blueman <daniel.blueman@...il.com>,
	Mat <jackdachef@...il.com>, LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Chris Mason <chris.mason@...cle.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	The development of BTRFS <linux-btrfs@...r.kernel.org>
Subject: Re: Btrfs: broken file system design (was Unbound(?) internal 
	fragmentation in Btrfs)

On Wed, Jun 23, 2010 at 8:43 PM, Daniel Taylor <Daniel.Taylor@....com> wrote:
> Just an FYI reminder.  The original test (2K files) is utterly
> pathological for disk drives with 4K physical sectors, such as
> those now shipping from WD, Seagate, and others.  Some of the
> SSDs have larger (16K0 or smaller blocks (2K).  There is also
> the issue of btrfs over RAID (which I know is not entirely
> sensible, but which will happen).
>
> The absolute minimum allocation size for data should be the same
> as, and aligned with, the underlying disk block size.  If that
> results in underutilization, I think that's a good thing for
> performance, compared to read-modify-write cycles to update
> partial disk blocks.

Block size = 4k

Btrfs packs smaller objects into the blocks in certain cases.
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