Date:	Thu, 2 Aug 2012 13:57:48 -0700
From:	Justin Maggard <jmaggard10@...il.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: resize2fs > 16TB questions

On Thu, Aug 2, 2012 at 1:15 PM, Andreas Dilger <adilger@...mcloud.com> wrote:
>
> On 2012-07-29, at 12:08, Arne Hüggenberg <hueggenberg@...rtsandbytes.de> wrote:
>
> > On Jul 29, 2012, at 8:30 PM, Andreas Dilger wrote:
> >>>> Unfortunately, the group descriptor size is not printed.
> >>>
> >>> how can i get the group descriptor size?
> >>
> >> Possibly with "debugfs stats"?
> >
> > ~ # debugfs /dev/vg0/lvol1
> > debugfs 1.42.4 (12-June-2012)
> > debugfs:  stats
> > debugfs:  stats
> >
> > Filesystem volume name:   <none>
> > Last mounted on:          /home/filestore_extern_1
> > Filesystem UUID:          8fba4f1b-5311-4c9b-b8bf-def4957dc1bd
> > Filesystem magic number:  0xEF53
> > Filesystem revision #:    1 (dynamic)
> > Filesystem features:      has_journal ext_attr resize_inode dir_index filetype extent 64bit flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
> > Filesystem flags:         signed_directory_hash
> > Default mount options:    user_xattr acl
> > Filesystem state:         clean
> > Errors behavior:          Continue
> > Filesystem OS type:       Linux
> > Inode count:              521011200
> > Block count:              4168089600
> > Reserved block count:     191127425
> > Free blocks:              2162482117
> > Free inodes:              520936736
> > First block:              0
> > Block size:               4096
> > Fragment size:            4096
> > Reserved GDT blocks:      60
> > Blocks per group:         32768
> > Fragments per group:      32768
> > Inodes per group:         4096
> > Inode blocks per group:   256
> > RAID stride:              16
> > RAID stripe width:        160
> > Flex block group size:    16
> > Filesystem created:       Fri Jul 27 17:16:24 2012
> > Last mount time:          Sun Jul 29 15:22:23 2012
> > Last write time:          Sun Jul 29 20:50:44 2012
> > Mount count:              6
> > Maximum mount count:      -1
> > Last checked:             Fri Jul 27 17:16:24 2012
> > Check interval:           0 (<none>)
> > Lifetime writes:          7662 GB
> > Reserved blocks uid:      0 (user root)
> > Reserved blocks gid:      0 (group root)
> > First inode:              11
> > Inode size:               256
> > Required extra isize:     28
> > Desired extra isize:      28
> > Journal inode:            8
> > Default directory hash:   half_md4
> > Directory Hash Seed:      ef2ec72a-750b-4822-bd8d-9117faadeaee
> > Journal backup:           inode blocks
> > Directories:              6392
> > Group  0: block bitmap at 2049, inode bitmap at 2065, inode table at 2081
> >           26585 free blocks, 4085 free inodes, 2 used directories, 4084 unused inodes
> >           [Checksum 0x7d46]
> > Group  1: block bitmap at 2050, inode bitmap at 2066, inode table at 2337
> >           4634 free blocks, 4096 free inodes, 0 used directories, 4096 unused inodes
> >           [Inode not init, Checksum 0x97aa]
> > Group  2: block bitmap at 2051, inode bitmap at 2067, inode table at 2593
> >           1020 free blocks, 4096 free inodes, 0 used directories, 4096 unused inodes
> >           [Inode not init, Checksum 0x571f]
> > Group  3: block bitmap at 2052, inode bitmap at 2068, inode table at 2849
> >           2047 free blocks, 4096 free inodes, 0 used directories, 4096 unused inodes
>
> Surprisingly, the group descriptor size is also not printed here. Looking at the code in mke2fs, it appears the 64-byte size used for filesystems when the 64bit flag is set, regardless of what size the filesystem is, and there is no way to change it.
>
> It looks like my theory is wrong, but I don't have access to a system to test this. Probably worthwhile to ask Yongqiang Yang (CC'd), who wrote the 64-bit resize code.
>

I had the same confusion 11 months ago, when the 64-bit resize
patchset was first posted, and I posted almost the same question here.
 My understanding at the end of the mailing list discussion was that
you still cannot resize your filesystem beyond 16TB -- even if the
64bit flag is set -- and you may never be able to do so on that
filesystem because you are using resize_inode and not meta_bg.  There
was a patchset posted on this list a few months ago by Yongquiang Yang
to do meta_bg expansion, but there hasn't been much action around it
from what I have seen (maybe for the 3.7 merge window?).

You can read on here:
http://permalink.gmane.org/gmane.comp.file-systems.ext4/27718

-Justin
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