linux-ext4 - Re: 5% diskspace used for ext4?

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Date:	Sun, 13 Jul 2008 18:41:12 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Christian Kujau <lists@...dbynature.de>
CC:	linux-ext4@...r.kernel.org
Subject: Re: 5% diskspace used for ext4?

Christian Kujau wrote:
> Hi,
> 
> I suspect this being a FAQ already, but I could not find[0] it:
> does ext4 really use 5% of available space for internal housekeeping? 
> After formatting and mounting a ~917GB partition I see:
> 
> # df -h /mnt/bench/
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sdb1             917G  200M  871G   1% /mnt/bench
> 
> The "200 MB used" would seem more sensible, but the difference between
> "available" and "size" is really 46 GB. How comes?
> 
> Thanks,
> Christian.
> 
> [0] http://ext4.wiki.kernel.org/index.php/Frequently_Asked_Questions
> 
> PS, a few more details how the filesystem got created and mounted:
> 
> # /opt/e2fsprogs/sbin/mkfs.ext4 -V
> mke2fs 1.41.0 (10-Jul-2008)
>  	Using EXT2FS Library version 1.41.0
> 
> # /opt/e2fsprogs/sbin/mkfs.ext4 /dev/sdb1
> [...]

Somewhere in [...] was:

XXX blocks (5.00%) reserved for the super user

this can be tuned and maybe should actually be on a sliding scale for
larger filesystems.

-Eric
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