linux-kernel - Re: [ANNOUNCE] DualFS: File System with Meta-data and Data Separation

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Message-ID: <p73sld7f96t.fsf@bingen.suse.de>
Date:	15 Feb 2007 21:38:18 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Juan Piernas Canovas <piernas@...ec.um.es>
Cc:	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	sfaibish <sfaibish@....com>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [ANNOUNCE] DualFS: File System with Meta-data and Data Separation

Juan Piernas Canovas <piernas@...ec.um.es> writes:

[playing devil's advocate here]

> If the data and meta-data devices of DualFS can be on different disks,
> DualFS is able to READ and WRITE data and meta-data blocks in
> PARALLEL.

XFS can do this too using its real time volumes (which don't contain
any metadata).  It can also have a separate log.

Also many storage subsystems have some internal parallelism
in writing (e.g. a RAID can write on different disks in parallel for
a single partition) so i'm not sure your distinction is that useful.

If you stripe two disks with a standard fs versus use one of them
as metadata volume and the other as data volume with dualfs i would
expect the striped variant usually be faster because it will give
parallelism not only to data versus metadata, but also to all data
versus other data.

Also I would expect your design to be slow for metadata read intensive
workloads. E.g. have you tried to boot a root partition with dual fs?
That's a very important IO benchmark for desktop Linux systems.

-Andi
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