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

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Date:	Thu, 28 Aug 2008 15:03:56 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	Eric Sandeen <sandeen@...hat.com>,
	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.
>   

I think a lot of high end customers still back up to tape (or virtual 
tape which is basically a tape emulation on top of RAID arrays), but 
they use commercial programs to do that.

> So a couple of comments.  First, it's probably not fair to use
> different backup programs for the different filesystems.  We probably
> want to do one set of comparisons where we use tar for all three.
> (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.)
>   

I like Chris's acp program since that is heavily optimized (read files 
in inode sorted order) and is small enough to tweak.

> 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.  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.  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.  :-)
>
>   

We may as well just time "tar" as an easy baseline.

> 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.
>
> 						- Ted
>   

Like acp ;-)

ric

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