[DRBD-user] DRBDv9 - some questions

Roland Kammerer roland.kammerer at linbit.com
Thu Sep 28 15:16:37 CEST 2017

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

On Thu, Sep 28, 2017 at 02:31:55PM +0200, Gandalf Corvotempesta wrote:
> Hi to all,
> Some questions about DRBDv9 (i'm really new to DRBD and DRBDv9 seems
> to be a major refactor):
> Let's assume a 3-node cluster
> a) should I use RAID or creating resources on raw-disks would be ok?

That is something you have to define for yourself. DRBD does not care,
but you do.

> b) can I use ZFS on top of DRBD ?

For now don't do that. Without details, for now that will make troubles
if  you don't do it right. The other way round is find. We have some
customers that use ZFS and split block devices out of ZFS and use these
as backing devices for DRBD.

> c) what if I have to aggragate multiple resources to increase spaces ?
> Can I use LVM with something like this:
> pvcreate /dev/drbd0
> pvcreate /dev/drbd1
> vgcreate vg0 /dev/drbd0 /dev/drbd1
> lvcreate .......
> to create a single LV on top of 2 drbd resources ?

You can. Again, DRBD does not care, if that is really what you want is
something different. If it's just about increasing, then you can
increase the backing devices (let's assume LVM here) and then you
drbadadm resize the drbd device.

> d) what If node0.disk0 on resource0 will fail and node0.disk1 on
> resource1 don't?
> My LV spawning both resource will still work as expect but in a little
> bit slow mode as drbd has to fetch missing data (due to failed disk0)
> from one of the other peer ?


> e) AFAIK drbd is a network block device, to access this "block device"
> should I put an NFS/iSCSI/Whatever in front of it or are there
> something integrated in drbd ? (Like NFS inside Gluster)

This again depends on your scenario. It's like having a /dev/sdX. You
can use it as a disk, our you expose the files on it via NFS. Now
s/sdX/drbdY/, nothing changes in the argumentation.

> f) a 3node cluster is still subject to splitbrain ?

Yes. You might want to check the fairly recently introduced "quorum"
setting for DRBD9.

Regards, rck

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