linux-kernel - Re: [PATCH v1 00/30] Ext4 snapshots

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Date:	Wed, 8 Jun 2011 18:01:45 +0300
From:	"Amir G." <amir73il@...rs.sourceforge.net>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org,
	tytso@....edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 00/30] Ext4 snapshots

On Wed, Jun 8, 2011 at 5:41 PM, Eric Sandeen <sandeen@...hat.com> wrote:
> On 6/8/11 9:04 AM, Amir G. wrote:
>>> And one last note, I also think that the snapshot format change in the
>>> > future, when we'll have snpashots with 64bit feature compatible seems
>>> > just wrong to me. Adding some features or changing the implementation a
>>> > bit is ok, but format change is different. When the code is upstream and
>>> > stable it is just wrong.
>> What can I say, I understand why it looks bad, but is 64bit code
>> upstream and stable? Hell no! e2fsprogs 64bit is not out yet!
>> There is no reason to call it 'format change'.
>> It's going to be a new format used only for 64bit fs, which are not
>> even out there yet. And when they are finally out there, they won't
>> have
>> snapshots until the new format is implemented.
>
> Well, the on-disk format for 64-bit (48-bit?) ext4 is there & fixed; it's
> just that there is no released userspace which can properly handle it, right?

I don't know, you tell me.
Are there many users out there using 64bit feature, without the proper
user space tools?

>
> I don't anticipate ext4 format changes for >16T, or am I missing something?
>
> -Eric
>

Argh! I wish I hadn't missed the Monday call (it's
not in a good time for me).
This whole 'format change' has gone out of control
and I find it hard to present my case properly on scattered emails.

The message I am trying to get through is:
There is 32bit snapshot file format, which is implemented and well tested.
There is 64bit snapshot file format, which is not implemented yet, so
64bit and snapshot feature are mutually exclusive.
If and when 64bit snapshot file format will be implemented, it will be
a new type of extent mapped file (v2) with 48bit logical addresses.
Is this a 'format change'? Call it what you will, but it shouldn't
affect anything on existing structures. It should only affect the
non-existing structure of 64bit snapshot file.

Does this answer your question?

Amir.
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