From: Theodore Tso Subject: Re: merging of two file system Date: Mon, 28 Jul 2008 16:04:39 -0400 Message-ID: <20080728200439.GL9378@mit.edu> References: <425904320807270905k32264faaq5c813b73000ee5c6@mail.gmail.com> <20080727225246.GD7922@mit.edu> <5feb302e0807281147y7362a227kb7d37d713be05296@mail.gmail.com> <425904320807281211y517f8847rc93cfa6a3a13aac3@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: rishi agrawal , linux-ext4@vger.kernel.org, listar@nl.linux.org To: Vineet Agarwal Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:51157 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751380AbYG1U3a (ORCPT ); Mon, 28 Jul 2008 16:29:30 -0400 Content-Disposition: inline In-Reply-To: <425904320807281211y517f8847rc93cfa6a3a13aac3@mail.gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Jul 29, 2008 at 12:41:25AM +0530, Vineet Agarwal wrote: > yeah i meant that we have to separate filesystems, > stored for example on /dev/hda1 and /dev/hda2, and we want to combine > the data in the two filesystems into a single filesystem /dev/hda3, or > combining the contents of /dev/hda2 so that it is also in /dev/hda1 > > so is there any mechanism exist to do so either online or offline . please help There is no direct way to do this. How big are the filesystems involved? The standard and easist way to do this would be to copy /dev/hda2 to another device, then if /dev/hda1 was created with on-line resizing inode, expanding /dev/hda1 to fill the space taken by /dev/hda2, and then simply use "cp" to copy the contents that had previously been in /dev/hda2 into the filesystem on /dev/hda1. In theory it would be possible to write a program would take to adjacent filesystems, and map out where the blocks would be once the two partitions were combined, and then relocate blocks to make a single filesystem. No one has done such a thing, however, for any filesytem. It is definitely not a trivial thing to do, but it is not impossible; it's not that different from some of what an off-line resize2fs operations does, albeit maybe 3-4 times more complex. The main thing is that no one has ever taken the time to do such a thing, because except for truly large filesystems, it's cheaper just to get an extra disk drive, and just copy the contents off, and then recreate the filesystem. - Ted