linux-kernel - Re: BTRFS: Unbelievably slow with kvm/qemu

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Message-ID: <20100902001859.GA4930@thunk.org>
Date:	Wed, 1 Sep 2010 20:18:59 -0400
From:	Ted Ts'o <tytso@....edu>
To:	"K. Richard Pixley" <rich@...r.com>
Cc:	Mike Fedyk <mfedyk@...efedyk.com>, Josef Bacik <josef@...hat.com>,
	Tomasz Chmielewski <mangoo@...g.org>,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	hch@...radead.org, gg.mariotti@...il.com,
	"Justin P. Mattock" <justinmattock@...il.com>, mjt@....msk.ru
Subject: Re: BTRFS: Unbelievably slow with kvm/qemu

On Tue, Aug 31, 2010 at 02:58:44PM -0700, K. Richard Pixley wrote:
>  On 20100831 14:46, Mike Fedyk wrote:
> >There is little reason not to use duplicate metadata.  Only small
> >files (less than 2kb) get stored in the tree, so there should be no
> >worries about images being duplicated without data duplication set at
> >mkfs time.
> My benchmarks show that for my kinds of data, btrfs is somewhat
> slower than ext4, (which is slightly slower than ext3 which is
> somewhat slower than ext2), when using the defaults, (ie, duplicate
> metadata).
> 
> It's a hair faster than ext2, (the fastest of the ext family), when
> using singleton metadata.  And ext2 isn't even crash resistant while
> btrfs has snapshots.

I'm really, really curious.  Can you describe your data and your
workload in detail?  You mentioned "continuous builders"; is this some
kind of tinderbox setup?

						- Ted
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