[DRBD-user] Can't shrink backing block device offline

[Christophorus Reyhan]

Hello,

I'm trying to shrink LVM backing block device offline because I
use internal metadata, and I'm following this guide
https://linbit.com/drbd-user-guide/drbd-guide-9_0-en/#s-shrinking-offline .
But it failed at create-md step.

*Here's the log for first machine (called ol1):*
[root at ol1 drbd.d]# e2fsck -f /dev/drbd0
e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/drbd0: 12/51200 files (0.0% non-contiguous), 109774/204732 blocks
[root at ol1 drbd.d]# drbdadm status
test role:Primary
  disk:UpToDate
  ol2 role:Secondary
    peer-disk:UpToDate

[root at ol1 drbd.d]# resize2fs /dev/drbd0 180M
resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/drbd0 to 184320 (1k) blocks.
The filesystem on /dev/drbd0 is now 184320 blocks long.

[root at ol1 drbd.d]# drbdadm down test
[root at ol1 drbd.d]# drbdadm dump-md test > /tmp/metadata
Found meta data is "unclean", please apply-al first
[root at ol1 drbd.d]# drbdadm apply-al test
[root at ol1 drbd.d]# drbdadm dump-md test > /tmp/metadata
[root at ol1 drbd.d]# lvreduce -L 180M /dev/mapper/vgdrbd-vol_drbd
  WARNING: Reducing active logical volume to 180.00 MiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce vgdrbd/vol_drbd? [y/n]: y
  Size of logical volume vgdrbd/vol_drbd changed from 200.00 MiB (50
extents) to 180.00 MiB (45 extents).
  Logical volume vgdrbd/vol_drbd successfully resized.
[root at ol1 drbd.d]# vi /tmp/metadata
[root at ol1 drbd.d]# blockdev --getsz /dev/mapper/vgdrbd-vol_drbd
368640
[root at ol1 drbd.d]# vi /tmp/metadata
[root at ol1 drbd.d]# drbdadm create-md test --max-peers=5
You want me to create a v09 style flexible-size internal meta data block.
There appears to be a v09 flexible-size internal meta data block
already in place on /dev/vgdrbd/vol_drbd at byte offset 188739584

Do you really want to overwrite the existing meta-data?
[need to type 'yes' to confirm] yes

md_offset 188739584
al_offset 188706816
bm_offset 188674048

Found ext3 filesystem
      184320 kB data area apparently used
      184252 kB left usable by current configuration

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
   * use external meta data (recommended)
   * shrink that filesystem first
   * zero out the device (destroy the filesystem)
Operation refused.

Command 'drbdmeta 0 v09 /dev/vgdrbd/vol_drbd internal create-md 5'
terminated with exit code 40
[root at ol1 drbd.d]# drbdadm create-md test
You want me to create a v09 style flexible-size internal meta data block.
There appears to be a v09 flexible-size internal meta data block
already in place on /dev/vgdrbd/vol_drbd at byte offset 188739584

Do you really want to overwrite the existing meta-data?
[need to type 'yes' to confirm] yes

md_offset 188739584
al_offset 188706816
bm_offset 188698624

Found ext3 filesystem
      184320 kB data area apparently used
      184276 kB left usable by current configuration

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
   * use external meta data (recommended)
   * shrink that filesystem first
   * zero out the device (destroy the filesystem)
Operation refused.

Command 'drbdmeta 0 v09 /dev/vgdrbd/vol_drbd internal create-md 1'
terminated with exit code 40

*Here's the log for second machine (ol2):*
[root at ol2 ~]# drbdadm down test
[root at ol2 ~]# rm /tmp/metadata
rm: remove regular file /tmp/metadata? y
[root at ol2 ~]# drbdadm dump-md test > /tmp/metadata
Found meta data is "unclean", please apply-al first
[root at ol2 ~]# drbdadm apply-al test
[root at ol2 ~]# lvreduce -L 180M /dev/mapper/vgdrbd-vol_drbd
  WARNING: Reducing active logical volume to 180.00 MiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce vgdrbd/vol_drbd? [y/n]: y
  Size of logical volume vgdrbd/vol_drbd changed from 200.00 MiB (50
extents) to 180.00 MiB (45 extents).
  Logical volume vgdrbd/vol_drbd successfully resized.
[root at ol2 ~]# vi /tmp/metadata

At this point, ol1 can't create-md so I stopped and restore the size back
to 200MB, then create-md, and succeeded.

Any help will be much appreciated.

-- 
Best Regards,
Christophorus Reyhan Tantio A.
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