From: Ted Ts'o <tytso@mit.edu>
To: Robin Dong <hao.bigrat@gmail.com>
Cc: Amir Goldstein <amir73il@gmail.com>, Tao Ma <taoma.tm@gmail.com>,
coly <colyli@gmail.com>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
Yongqiang Yang <xiaoqiangnk@gmail.com>
Subject: Re: Question about writable ext4-snapshot
Date: Sun, 22 Jan 2012 22:21:43 -0500 [thread overview]
Message-ID: <20120123032143.GA16363@thunk.org> (raw)
In-Reply-To: <CAFZ0FUXK89LLOmRGuXWW1UAZo0ydTi_O=383E+nsCywQgYh6eQ@mail.gmail.com>
On Sun, Jan 22, 2012 at 11:31:31AM +0800, Robin Dong wrote:
> > At the end of the day, thinp target is a very powerful tool, but
> > is does not fit all use cases. In particular, it fragments the
> > on-disk layout of ext4 metadata and benchmark results for how this
> > affect performance were never published.
Amir,
Well, to be fair, your approach to snapshotting also causes
fragmentation. If a file or a directory in the base image gets
modified while there is a read-only snapshot, the inode in the base
image gets fragmented as a result.
It is true that thin provisioning in general tends to defeat the block
placement algorithms used by a file system, but it will be possible to
create snapshots of non-thinp volumes, which will address this issue.
Hopefully in the next 3-6 months, these things will be implemented
enough so that we can benchmark them and see for certain how well or
poorly this approach will work out. I'm sure there will be a certain
number of tradeoffs for both approaches.
Regards,
- Ted
next prev parent reply other threads:[~2012-01-23 3:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-21 2:45 Question about writable ext4-snapshot Robin Dong
2012-01-21 4:24 ` Theodore Tso
2012-01-21 4:37 ` Andreas Dilger
2012-01-21 16:09 ` Amir Goldstein
2012-01-22 3:31 ` Robin Dong
2012-01-23 3:21 ` Ted Ts'o [this message]
2012-01-23 20:08 ` Amir Goldstein
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