linux-ext4 - Re: mkfs.ext4: high default -i value undocumented

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Message-ID: <49ADCEBB.6080904@redhat.com>
Date:	Tue, 03 Mar 2009 18:43:39 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	linux-ext4@...r.kernel.org, kzak@...hat.com
Subject: Re: mkfs.ext4: high default -i value undocumented

Jan Engelhardt wrote:
> On Wednesday 2009-03-04 00:19, Eric Sandeen wrote:
>>> Creating an ext4 filesystem on a 4 GB image file (to be loop-mounted 
>>> later) gives me 256K inodes. Choosing -i 4096 instead gives 1M, which 
>>> would mean the default for -i is 16384. 
>> That's right, look in /etc/mke2fs.conf:
>>
>> [defaults]
>>        base_features =
>> sparse_super,filetype,resize_inode,dir_index,ext_attr
>>        blocksize = 4096
>>        inode_size = 256
>>        inode_ratio = 16384
> 
> Interesting - thanks for the hint.
> 
>>> Besides me finding 16384 a 
>>> little unreasonable (XFS offers 2M inodes by default), 
>> XFS is a totally different beast, because it dynamically allocates
>> inodes.  It doesn't really offer *anything* by default.
>>
>> Which part of a 16384-data-bytes-to-inode-count ratio do you find
>> unreasonable?  Do you find it unreasonably high, or unreasonably low?
> 
> I think it's a bit too high, causing the amount of usable inodes
> to be a bit too low. 

When we doubled the size of inodes by default, we halved the count.  I
also have a sneaking suspicion that it may be too low for some
scenarios, but probably ok for most.

>>> the big 
>>> point is that the mke2fs manpage (belonging to util-linux, hence Cc) 
>> not so much:
>> $ rpm -qf /usr/share/man/man8/mke2fs.8.gz
>> e2fsprogs-1.41.3-2.fc10.x86_64
> 
> Sorry, I had looked for man8/mkfs.ext2.8.gz. I am not quite sure
> what makes some developers deviate(*) from the mkfs.$name/fsck.$name
> scheme ;-)

$ rpm -qf /usr/share/man/man8/mkfs.ext2.8.gz
e2fsprogs-1.41.3-2.fc10.x86_64

:)

> (*) e2, reiser(3), dosfs
> 
>>> does not mention this 16384 default.
>>> Hope this can be addressed.
>> You could send a patch :)
> 
> parent b2ca48f40eb33bd86b8d53d4373e7fce96bced4a (v1.41.4)
> commit ca28058c4004ceaa42edeb6ba61bc2aa53d7c03d
> Author: Jan Engelhardt <jengelh@...ozas.de>
> Date:   Wed Mar 4 01:36:09 2009 +0100
> 
> doc: mention default for mke2fs -i

thanks :)  (up to Ted now)

-Eric
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