[DRBD-user] Content of DRBD volume is invalid during sync after disk replace

[Lars Ellenberg]

On Mon, Jul 23, 2018 at 02:46:25PM +0200, Michal Michaláč wrote:
>                  Hello,
> 
>  
> 
> after replacing backing device of DRBD, content of DRBD volume (not only
> backing disk) is invalid on node with inconsistent backing device, until
> sync finishes. I think, correct behaviour is to read data from peer's
> (consistent) backing device if process running on node with inconsistent
> backing device wants to read unsynchronized part of DRBD volume.

...

> If I  skip create-md (step 4), situation is even worse - after attach disk,
> DRBD says volume is sychronized(!):
> 
> log: Began resync as SyncTarget (will sync 0 KB [0 bits set])
> 
> but after verification (drbdadm verify test), there are many out-of-sync
> sectors. 
> 
> After disconnect/connect volume test, resync not started(!):
> 
> log: No resync, but 3840 bits in bitmap!
> 
> If I (on new DRBD volume) just disconnect -> write changes to primary ->
> connect, sync works correctly.

> Versions (on both nodes are identical): 
> # cat /proc/drbd
> version: 9.0.14-1 (api:2/proto:86-113)
> GIT-hash: 62f906cf44ef02a30ce0c148fec223b40c51c533 build by root at n2,
> 2018-07-12 13:18:02
> 
> Transports (api:16): tcp (9.0.14-1)
> 
> # uname -a
> Linux n2 4.15.17-1-pve #1 SMP PVE 4.15.17-9 (Wed, 9 May 2018 13:31:43 +0200)
> x86_64 GNU/Linux
> 
> # lvm version
>   LVM version:     2.02.168(2) (2016-11-30)
>   Library version: 1.02.137 (2016-11-30)
>   Driver version:  4.37.0

> Is it bug or am I doing something wrong?

Thanks for the detailed and useful report,
definetely a serious and embarassing bug,
now already fixed internally.
Fix will go into 9.0.15 final.
We are in the progress of making sure
we have covered all variants and lose ends of this.

-- 
: Lars Ellenberg
: LINBIT | Keeping the Digital World Running
: DRBD -- Heartbeat -- Corosync -- Pacemaker

DRBD® and LINBIT® are registered trademarks of LINBIT
__
please don't Cc me, but send to list -- I'm subscribed