linux-ext4 - Re: Do we need dump for ext4?

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Message-ID: <48B6F8E8.8090308@redhat.com>
Date:	Thu, 28 Aug 2008 14:13:44 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	ext4 development <linux-ext4@...r.kernel.org>,
	Ric Wheeler <rwheeler@...hat.com>
Subject: Re: Do we need dump for ext4?

Theodore Tso wrote:
> On Thu, Aug 28, 2008 at 09:58:10AM -0500, Eric Sandeen wrote:
>> I was talking to Ric about dump benchmarks, and he was of the impression
>> that dump may not be used that often anymore, at least in the
>> enterprise.
> 
> Many people don't use the dump/restore any more program any more,
> that's definitely true.  Whether people use backups (as opposed to
> large amounts of RAID) in the enterprise is a different question.  I'm
> not so sure about the second question.
> 
> So a couple of comments.  First, it's probably not fair to use
> different backup programs for the different filesystems.  

Well, if a filesystem has a dedicated, presumably optimized backup
utility, why would you not benchmark that as part of the mix? :)

> We probably
> want to do one set of comparisons where we use tar for all three.

Yep, I'm doing that now ... also realized I tested on an inappropriate
elevator (cfq) for a fancy-raid.  I'll resend in a bit.

> (Note: not all backup/dump programs are doing the right things with
> xattr's, so we're not necessarily comparing programs with completely
> identical functionality.)

well, tar supposedly is with the options I gave it, xfsdump certainly
does, and dump, I dunno offhand.

> Secondly, it really wouldn't be hard to update dump/restore for ext4.
> It uses libext2fs, so the real problem is that it is explicitly
> checking the feature flags.  Removing those checks may be all that is
> necessary, given that ext2_block_iterate() still works for
> extent-based files.  

Eh, I'll test that then.

> I just noted BTW that the dump/restore doesn't
> seem to be TOTALLY abandoned.  It was last updated in 2006, true, but
> there is support for backing up and restoring extended attributes and
> ACL's.  

Ah, ok, so they all should be backing up acls/attrs then.

> I wonder if they broke format compatibility with BSD 4.4
> format dump/restore backups when they did it --- and if anyone would
> still cares.  :-)
> 
> Finally, I suspect most of the problem with using tar is the HTREE
> dirent sorting problem.  If we modify tar to sort the directory
> entries before emitting the files, and then use that tar across all
> the filesystems, I suspect the results would be much more better for
> ext3 and ext4.

True enough, just testing what we have now.  I can play with acp...

-Eric
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