Date:	Sun, 29 Jul 2012 09:11:03 -0700
From:	Andreas Dilger <adilger@...mcloud.com>
To:	Arne Hüggenberg <hueggenberg@...rtsandbytes.de>
Cc:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: resize2fs > 16TB questions

On 2012-07-29, at 8:24, Arne Hüggenberg <hueggenberg@...rtsandbytes.de> wrote:
> 
> im trying to resize a ext4 fs to > 16TB.

Unfortunately, this is not possible today without advance planning.  There are some structures on disk (group descriptors) that need to be larger for 64-bit filesystems. It is possible to format a 32-bit filesystem with larger group descriptors using the "-O 64bit" option, but this doesn't happen by default today. 

Possibly we should start using the 64-byte group descriptors by default for filesystems over, say, 4 TB, so they can be resized beyond 16 TB.

It might also be possible to modify resize2fs to change the group descriptor size, but that isn't possible today. 

> Having had a look at the e2fsprogs 1.42.x release notes i thought that, with the online resize ioctl having been merged in Kernel 3.3, this should be possible.
> 
> But so far i have had no success achieving this:
> 
> ~ # uname -a
> Linux 3.3.8-gentoo #1 SMP Fri Jul 27 16:13:25 CEST 2012 x86_64 Intel(R) Xeon(R) CPU E5620 @ 2.40GHz GenuineIntel GNU/Linux
> 
> ~ # tune2fs -l /dev/vg0/lvol1
> tune2fs 1.42.4 (12-June-2012)
> 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 needs_recovery extent 64bit flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize

Was the filesystem formatted with the 64bit option, or was this enabled after formatting time?  This puts my earlier comment in doubt. 

> 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:              2195165566
> Free inodes:              520937830
> 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 15:22:23 2012
> Mount count:              6
> Maximum mount count:      -1
> Last checked:             Fri Jul 27 17:16:24 2012
> Check interval:           0 (<none>)
> Lifetime writes:          7485 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

Unfortunately, the group descriptor size is not printed.  

> ~ # vgdisplay
>  --- Volume group ---
>  VG Name               vg0
>  System ID             
>  Format                lvm2
>  Metadata Areas        2
>  Metadata Sequence No  4
>  VG Access             read/write
>  VG Status             resizable
>  MAX LV                0
>  Cur LV                1
>  Open LV               1
>  Max PV                0
>  Cur PV                2
>  Act PV                2
>  VG Size               18.18 TiB
>  PE Size               4.00 MiB
>  Total PE              4766718
>  Alloc PE / Size       4766718 / 18.18 TiB
>  Free  PE / Size       0 / 0   
>  VG UUID               q6p5LG-pi1P-pAcI-fSsv-vFI7-6sAA-eabaBH
> 
> ~ # lvdisplay
>  --- Logical volume ---
>  LV Name                /dev/vg0/lvol1
>  VG Name                vg0
>  LV UUID                7OF1do-HqZD-FGSN-chJF-rPYC-x1Ty-vGCZlc
>  LV Write Access        read/write
>  LV Status              available
>  # open                 1
>  LV Size                18.18 TiB
>  Current LE             4766718
>  Segments               2
>  Allocation             inherit
>  Read ahead sectors     auto
>  - currently set to     256
>  Block device           254:1
> 
> ~ # resize2fs /dev/vg0/lvol1
> resize2fs 1.42.4 (12-June-2012)
> resize2fs: New size too large to be expressed in 32 bits

This may just be a hard-coded check built into resize2fs, but may be over-zealous of the filesystem was formatted with -O 64bit. 

> Any advice on how to proceed would be welcome.
> 
> Regards,
> Arne
> 
> 
> 
> 
> 
> 
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