inode size for coreos, ext4 is set to 128 than default 256. Reqeusting explanation

[Himanshu Khurana]

tune2fs -l /dev/xvda9
Inode size:              128

while as per   /etc/mke2fs.conf

    }
    ext4 = {
        features = has_journal,extent,huge_file,flex_bg,uninit_bg,64bit,dir_nlink,extra_isize
        inode_size = 256
    }

Please explain.

[David Michael]

It is using the default from the ChromeOS disk formatting scripts:
https://github.com/coreos/scripts/blob/master/build_library/disk_util#L394

Thanks.

David

[Alex Crawford]

On 02/20, David Michael wrote:
> It is using the default from the ChromeOS disk formatting scripts:
> https://github.com/coreos/scripts/blob/master/build_library/disk_util#L394

This was actually changed by us a while ago. From the commit (d09aeb36):

> This change changes the default 'bytes-per-inode' ration from 16K to 4K,
> the block size. To prevent this from wasting too much space change the
> inode size from the default 256 to the minimum size, 128. Larger inodes
> are used to store extended attributes more efficiently but since we do
> not use SELinux the majority of files do not have security attributes.

This was done to fix the issue of excessive inode usage [1]. This might
be worth revisiting now that we use SELinux and docker has since moved
to overlay2.

-Alex

[1]: https://github.com/coreos/bugs/issues/264