linux-ext4 - Re: [CALL FOR TESTING] Make Ext3 fsck way faster [2.6.24-rc6 -mm patch]

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Date:	Tue, 15 Jan 2008 23:25:38 -0500
From:	Valdis.Kletnieks@...edu
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Abhishek Rai <abhishekrai@...gle.com>,
	linux-kernel@...r.kernel.org, rohitseth@...gle.com,
	linux-ext4@...r.kernel.org
Subject: Re: [CALL FOR TESTING] Make Ext3 fsck way faster [2.6.24-rc6 -mm patch]

On Tue, 15 Jan 2008 03:04:41 PST, Andrew Morton said:

> In any decent environment, people will fsck their ext3 filesystems during
> planned downtime, and the benefit of reducing that downtime from 6
> hours/machine to 2 hours/machine is probably fairly small, given that there
> is no service interruption.  (The same applies to desktops and laptops).

I've got multiple boxes across the hall that have 50T of disk on them, in one
case as one large filesystem, and the users want *more* *bigger* still (damned
researchers - you put a 15 teraflop supercomputer in the room, and then they
want someplace to *put* all the numbers that come spewing out of there.. ;)

There comes a point where that downtime gets too long to be politically
expedient.  6->2 may not be a biggie, because you can likely get a 6 hour
window.  24->8 suddenly looks a lot different.

(Having said that, I'll admit the one 52T filesystem is an SGI Itanium box
running Suse and using XFS rather than ext3).

Has anybody done a back-of-envelope of what this would do for fsck times for
a "max realistically achievable ext3 filesystem" (i.e. 100T-200T or ext3
design limit, whichever is smaller)?

(And one of the research crew had a not-totally-on-crack proposal to get a
petabyte of spinning oxide.  Figuring out how to back that up would probably
have landed firmly in my lap.  Ouch. ;)

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