linux-ext4 - Re: flex_bg with tune2fs posible?

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Date:	Sat, 9 Apr 2011 17:01:53 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Santiago Garcia Mantinan <manty@...ty.net>
Cc:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: flex_bg with tune2fs posible?

On 2011-04-09, at 3:50 PM, Santiago Garcia Mantinan <manty@...ty.net> wrote:
> I had converted an ext3 filesystem to ext4 long ago but comparing it's
> features with the ones found on a newly formatted ext4 filesystem I found
> that I had these features missing:
> flex_bg huge_file dir_nlink extra_isize

> Current doc at ext4.wiki.kernel.org says: "There are additional ext4
> features, such as flex_bg and > 16TB filesystem support that can only
> be enabled at format time via mke2fs."
> 
> I did activate all these 4 without any problem (2.6.38 with 1.41.12
> e2fsprogs) is the doc old and doesn't reflect that this is now possible?
> 
> Or have I done something I'll regret?

Technically, flex_bg can be activated after the filesystem is formatted, but it doesn't actually provide the benefit as if enabled at format time.

The dir_nlink and huge_file features can safely be enabled on an existing filesystem, allowing > 64000 subdirs and > 2 TB files, respectively. 

The extra_isize feature will not itself do anything if the filesystem wasn't formatted with large inodes (>128 bytes), though it is possible this was done even for ext3, depending on the version of e2fsprogs used. 

> So far the filesystem seems ok (e2fsck doesn't detect any problems) and
> files seem ok as well.
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