[DRBD-user] Error create filesystem on active node in 3-three node configuration

[Felix Frank]

Hi,

On 03/24/2011 01:10 PM, Михаил Евстратов wrote:
> Hi!
> 
> I have three-node configuration.
> (Like this
> http://www.howtoforge.com/drbd-8.3-third-node-replication-with-debian-etch)
> 
> When I run
> 
> drbdadm --stacked down r0-U
> and
> mkfs.ext3 /dev/drbd0

uhm...did you create an fs on the lower DRBD?

Don't do that. This is the same as creating metadata on a simple DRBD
and then formatting the backing device instead of the DRBD proper.

Bring up the stacking DRBD and mke2fs on that.

> and run
> drbdadm --stacked up r0-U
> 
> an error
> 
> drbdadm --stacked up r0-U
> 10: Failure: (119) No valid meta-data signature found.
> 
>         ==> Use 'drbdadm create-md res' to initialize meta-data area. <==
> 
> Command 'drbdsetup 10 disk /dev/drbd0 /dev/drbd0 internal --set-defaults
> --create-device' terminated with exit code 10

You made an fs on the lower device, which is sort of the backing device,
thus destroying the *upper* device's metadata.

> If I run
> 
> drbdadm --stacked create-md r0-U
> 
> an error
> 
> md_offset 536847597568
> al_offset 536847564800
> bm_offset 536831180800
> 
> Found ext3 filesystem
>    524265236 kB data area apparently used
>    524249200 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 10 v08 /dev/drbd0 internal create-md' terminated with
> exit code 40
> drbdadm create-md r0-U: exited with code 40

The erroneously created filesystem is now in your way. There is no room
left to create metadata.

When stacking, the upper device's metadata is physically in front of the
original (lower device's) metadata.

Scrap the fs, create metadata for your stacking device and mke2fs *on
that device*. You will be fine then.

HTH,
Felix