linux-ext4 - Re: Which kernel do I need to use ext4 64-bit.

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Message-ID: <09799e83-6a68-58e5-0cdf-eb4bb815bd39@gmail.com>
Date:   Tue, 18 Jul 2017 19:23:19 -0500
From:   Ram Ramesh <rramesh2400@...il.com>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org
Subject: Re: Which kernel do I need to use ext4 64-bit.

On 07/18/2017 06:31 PM, Theodore Ts'o wrote:
> On Tue, Jul 18, 2017 at 05:49:31PM -0500, Ram Ramesh wrote:
>> Thanks. I can't update e2fsprogs to 1.43 without knowing that the file
>> system it creates can be mounted on my kernel. I am with ubuntu 14.04 which
>> only has these. I could manually download and build from source or install
>> from another repository only if I know my kernel will support it. So, I
>> really need to know if linux 3.13 support ext4-64bit.
> Why are you not willing to update to Ubuntu 16.04, or something less
> ancient?  The 64-bit feature is "supported" in the sense that the
> kernel will understand it.  But if you have a paid support contract
> from Canonical, you need to ask them if they will "support" it.  And
> if you are hoping that the upstream kernel development community will
> provide you free "support" for an ancient enterprise distribution, you
> need to understand that this is best efforts only.
>
> Technically speaking it appears that Linux 3.13 understands the 64-bit
> feature.  Whether there are any critical bugs that have since been
> fixed is a very different question.  Technically speaking, e2fsprogs
> 1.42.9 also understands the 64-bit feature, but I *know* that there
> are a number of off-line resize bugs with the 64-bit features in the
> 1.42.x e2fsprogs line.
>
> The reason to use 1.43.x is that it will turn on the 64-bit feature
> "automatically".  But you could just also reformat the file system
> using "mke2fs -t ext4 -O 64bit /dev/xxx" using 1.42.x.  Also note that
> depending on which repository that you download e2fsprogs 1.43.x, you
> may need to edit /etc/mke2fs.conf so mke2fs doesn't enable the
> metadata_csum feature by default (which will not be supported by Linux
> 3.13).
>
> So it might be that the safer thing to do is to build e2fsprogs 1.43.x
> (so you get the latest bug fixes), and then check the /etc/mke2fs.conf
> file to make sure it will create the same sort of file system as 1.42.x.
>
> But if this is a critical enterprise/production system, and you are
> expecting support by sending e-mail to linux-ext4@...r.kernel.org, I
> do feel morally bound to dissuade you from doing that unless you are
> prepared to carry most of the support burden yourself.  There is a
> reason why companies pay $$$ to Red Hat or SuSE...
>
> Cheers,
>
> 						- Ted
Thanks for the details. Sorry, if I asked inappropriate questions that 
angered/annoyed any one. I thought I was simply checking with the 
experts. Andreas told me a simple method is to create a filesystem and 
test it. I was too dumb to think of that method first, instead of asking.

I am with 14.04 because it is supposed to be LTS and last time I changed 
too quickly (that is from 12.04 to 14.00, I had everything fall apart 
due to various release bugs) This time I am letting 16.04 chill a bit 
before switching. I would have done it earlier, but that too does not 
have efs2progs 1.43. Only 16.10 has. That is too hot for me.

This is my personal system for running DVR with mythtv. No enterprise 
here and no $$$ here either. Just some one willing to ask questions when 
needed.

Ramesh