Date: Sun, 29 Jun 2003 14:26:04 -0400
From: rmoser <mlmoser@comcast.net>
Subject: Re: File System conversion -- ideas
In-reply-to: <200306291011.h5TABQXB000391@81-2-122-30.bradfords.org.uk>
To: John Bradford <john@grabjohn.com>, linux-kernel@vger.kernel.org
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On 6/29/2003 at 11:11 AM John Bradford wrote:

>> Anyhow, I'm thinking still about when reiser4 comes out.  I want to
>> convert to it from reiser3.6.  It came to my attention that a user-space
>> tool to convert between filesystems is NOT the best way to deal with
>> this. Seriously, you'd think it would be, right?  Wrong, IMHO.
>>
>> You have the filesystem code for every filesystem Linux supports.  It's
>> there, in the kernel.  So why maintain a kludgy userspace tool that has
>> to be rewritten to understand them all?  I have a better idea.
>>
>> How about a kernel syscall?  It's possible to do this on a running
>> filesystem but it's far too difficult for a start, so let's start with
>> unmounted filesystems mmkay?
>
>Apart from the special case of converting from one major version of a
>filesystem to another major version of the same filesystem, I think
>the performance of an on-the-fly filesystem conversion utility is
>going to be so much worse than just creating a new partition and
>copying the data across, that the only reason to do it would be if you
>could do it on a read-write filesystem without unmounting it.
>

You've entirely missed the point :/  Did you read the last section?  I noted
that the "make new partition and copy" method requires, first off, space
for a new partition.  All my partitions have massive amount of data on them.
I can't do that.  Those of us that can have to either do it twice, or rewrite
fstab.

Eventually I'm hoping it can be done on a read-write filesystem.  It's
possible; I've thought about how to defragment read-write datasystems
without getting in the way of logical operations.

>What I'd like to see is union mounts which allowed you to mount a new
>filesystem of a different type over the original one, and have all new
>writes go to the new fileystem.  I.E. as files were modified, they
>would be re-written to the new FS.  That would be one way of avoiding
>the performance hit on a busy server.
>

mmmm, then you'd need both fs' though.  That's not conversion ;-)


>John.
>-
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