[ClusterLabs] Antw: [EXT] Re: Removing DRBD w/out Data Loss?

[Ulrich Windl]

>>> Valentin Vidic <vvidic at valentin-vidic.from.hr> schrieb am 09.09.2020 um
22:15
in Nachricht <20200909201543.GV8773 at valentin-vidic.from.hr>:
> On Wed, Sep 09, 2020 at 12:10:54PM +0000, Eric Robinson wrote:
>> With DRBD stopped, wipefs only showed one signature...
>> 
>> [root at 001db01 ~]# wipefs /dev/vg0/lv0
>> offset               type
>> ‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑‑
>> 0x438                ext4   [filesystem]
>>                      UUID:  2035aabe‑b6e1‑4313‑a022‑9518eb7489e6
>> 
>> So I just mounted the filesystem...
>> 
>> [root at 001db01 ~]# mount /dev/vg0/lv0 /mnt
>> [ 7712.478905] EXT4‑fs (dm‑2): 35 orphan inodes deleted
>> [ 7712.484594] EXT4‑fs (dm‑2): recovery complete
>> [ 7712.506344] EXT4‑fs (dm‑2): mounted filesystem with ordered data mode. 
> Opts: (null)
>> 
>> ...and all my data seems to be there? Did I miss something? I don't
>> understand. Where did the DRBD partition go?
> 
> DRBD metadata is always at the end of the device (or on a different
> device if DRBD configuration sets external metadata parameter) so
> the filesystem should be directly accessible once the drbd signature
> is wiped. This also means it is possible to add DRBD to an existing
> partition (if there is enough free space at the end or using an
> external device).

But doesn't hat make resizing the volume a big mess (similar to resizing GPT
disks)?

> 
> I get a different output and behavior on Debian 10 (kernel 4.19,
> DRBD 8.4.10, drbd‑utils 9.5.0):
> 
> # wipefs /dev/vg0/drbd
> DEVICE OFFSET     TYPE UUID                                 LABEL
> drbd   0x3ffff03c drbd 4c26a7436a17d14                      
> drbd   0x438      ext4 b708b27c‑f6a6‑4f07‑8417‑8c17d8a2febb 
> 
> # mount /dev/vg0/drbd /mnt
> mount: /mnt: unknown filesystem type 'drbd'.
> 
> # wipefs ‑o 0x3ffff03c /dev/vg0/drbd
> /dev/vg0/drbd: 4 bytes were erased at offset 0x3ffff03c (drbd): 83 74 02 6c
> 
> # wipefs /dev/vg0/drbd
> DEVICE OFFSET TYPE UUID                                 LABEL
> drbd   0x438  ext4 b708b27c‑f6a6‑4f07‑8417‑8c17d8a2febb 
> 
> # mount /dev/vg0/drbd /mnt
> 
> ‑‑ 
> Valentin
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