From: Mingming Cao <cmm@us.ibm.com>
Subject: Re: [PATCH 3/8][e2fsprogs] add new -D <desc-size> option to mkfs
Date: Fri, 31 Aug 2007 17:25:00 -0700
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Cc: Valerie Clement <valerie.clement@bull.net>,
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	"Theodore Ts'o" <tytso@mit.edu>
To: Andreas Dilger <adilger@clusterfs.com>
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On Thu, 2007-08-30 at 14:51 -0600, Andreas Dilger wrote:
> On Aug 30, 2007  12:12 -0700, Mingming Cao wrote:
> > On Thu, 2007-08-30 at 17:37 +0200, Valerie Clement wrote:
> > > This patch adds a new option -D <descriptor-size> to mkfs to allow creating
> > > ext4 filesystems with larger group descriptor size.
> > > 
> > > By default, the group descriptor size is 32 bytes.
> > > To support 64-bit physical block numbers and thus to be able to use filesystems
> > >  > 16TB, the group descriptor size must be increased to 64 bytes.
> > 
> > Could you explain a bit more why we need this option? It seems to me we
> > could make the block group descriptor size to 64bytes whenever creating
> > a ext4 filesystem by default. Is there any case we need to create ext4
> > with old 32 bytes block group descriptors?
> 
> Because we will only have a single tool "mke2fs", and it should be able
> to format filesystems for all kernels.

I agree. I was wondering why not make the 64bytes block group descriptor
for ext4 as default. So by default we don't need to specify the size
when creating ext4 fs.

> Also, it may be desirable to
> make the descriptor larger for whatever reason (e.g. testing some new
> feature).
> 
Okay, that could be useful for ext4. Don't feel ext2/3 needs that
option.

Regards,

Mingming