[DRBD-user] 4TB limit

Ralf Gross Ralf-Lists at ralfgross.de
Fri Oct 20 09:16:44 CEST 2006


Steven Wilton schrieb:
> 
> > if I understand the documentation correct, there is a limit of ~4TB
> > for a single drbd device on 32bit systems. Furthermore lvm on top of a
> > drbd device is not recommended.
> > 
> > What is the recommended way to use drbd and lvm for filesystems that
> > are >4TB. My aim would be to have only one mount point, hence lvm on
> > top of drbd would be desired.
> > 
> 
> LVM on top of DRBD causes problems because LVM sees the signatures
> on the disks before DRBD starts and tries to use the disks directly.

I could solve this with a filter expression in my lvm.conf. Now I have
3 drbd devices in one lvm vg. I started with 2 devices, created the
pv, vg, lv and the ext3 filesystem. Then I added the 3. device with
pvcreate, vgextend, lvextend, e2fsck and resize2fs. No problem so far.
 
> I thought the "correct" fix for this was to put DRBD on top of LVM
> (that's what we do here).

Both solutions work, but I think lvm on top of drbd is preferable.

http://article.gmane.org/gmane.comp.linux.drbd/6175

For me it's more logical to have the lvm on top of drbd and the
filesystem on top of lvm.

But I'm a bit worried which nasty things can happen with this setup
and what to to then in the right order.

Does anyone have some real life examples of possible failurs?

Ralf



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