[DRBD-user] Meta Disk

Lars Ellenberg Lars.Ellenberg at linbit.com
Wed Sep 6 19:27:11 CEST 2006

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

/ 2006-09-06 16:14:08 +0000
\ Eddie Mbabaali:
> I am trying to use drbd for NFS servers that are running on SLES 10. There was
> no separate partition created for the meta files during install but I have alot
> of space available. I can not repartition the servers because they are in
> production and I fear to encounter data loss/recovery issues.

> Is it possible to create the block devices without losing any data or
> resizing existing filesystems.

you either have to create a dedicated meta data partition
with at least 128 MiB, or use drbd with internal meta data.
the internal meta data will overwrite (DESTROY) the last 128 MiB
(aligned to a multiple of 8 sectors (4kiB)).

so, if your file system currently uses the full partition size it is
living on, and you cannot create a dedicated partition for drbd meta
data, and you cannot (or don't want to) shrink (resize) the existing
file system, you have no place for drbd to put its meta data.
so you cannot use drbd.

if you ignore this, and use drbd with internal meta data,
it might apear to work now, but even while things apear to be still
working it had already corrupted your file system, possibly caused not
recoverable loss of important data, and it _will_ crash sooner or later.

depending on where your "lot of space available" is,
you are out of luck.

if you used lvm, things would be much easier,
you'd just create an additional lv in the free space.

if you still have free space of at least 128 MB in the as yet
unpartitioned area of the disk, you could just create a partition there,
and reboot (you cannot reread the partition table when you have
mounted file systems on that disk).

if you don't have free unpartitioned space, you need to shrink the
file system or get that space for the meta data partition elsewhere.

> Can I actually use drbd with a sym link /dev/drbX /mnt/reports ?

complete misconception.
you mix up block devices, device nodes,
file systems, mount points and symlinks all at once.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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