should each VM have its own DRBD or one DRBD for all VMs?

[PepeOnaChair]

Hi,

I`ve heard that it is much safer, to setup separate DRBD resource for each single VM. So each VM has its own LV with DRBD. Is this really safer setup? It is much more complicated and more work/configuring has to be done But when some bad things happen to cluster (2 node cluster, HA) would this kind of setup lead to _higher_probability_ that in case of split-brain, it will hit just some of DRBD instances? So at least some of VMs would survive without any problem.

If there would be just one DRBD instance with a lot of LV volumes with VMs on them, split-brain would affect all of them.

Thank you
Pep.

 

[adamb]

I think its best to have two DRBD resources in a 2 node setup. This way node 1 always own's drbd0 and node2 always own's drbd1. In the case of a split brain, there is no question as to what host owns what. Having a DRBD partition for each VM is something I have never seen done.

 

[mo_]

consider that for a 2 node setup you absolutely need an external quorum disk since without it 1 node going down means losing quorum and you REALLY dont want that to happen. Now to my understanding you will need a quorum disk for every DRBD pair you set up and while they hardly take up any space on the (third) server you put them on, it still means even more configuration work.

Sadly I cannot comment on performance differences between those 2 options.

What I can say is that if you use a single storage device (say a raid device or an LVM device) for all DRBD volumes (on one node) the likelyhood that any hardware or network failure will disconnect ALL DRBD pairs is 100%, so in that case it would not help prevent some split brains

 

[PepeOnaChair]

thank you for your replies...
But anyway, is it somehow possible to add DRBD device directly to Proxmox (I've installed ver. 2.3 already) as a "Storage"? I mean not as LMV_on_the_top_of_DRBD storage. So I will not need to create LVM Physical Volume on the top of DRBD and add it as "LVM group" into Proxmox storages. I know that DRBD devices can be used as a physical disks for installing VMs straight onto, so why not to have this option in Proxmox?
Any idea?

 

[e100]

thank you for your replies...
But anyway, is it somehow possible to add DRBD device directly to Proxmox (I've installed ver. 2.3 already) as a "Storage"? I mean not as LMV_on_the_top_of_DRBD storage. So I will not need to create LVM Physical Volume on the top of DRBD and add it as "LVM group" into Proxmox storages. I know that DRBD devices can be used as a physical disks for installing VMs straight onto, so why not to have this option in Proxmox?
Any idea?

The reason this is not supported in Proxmox is because it falls under the category of "unnecessary complexity"

Do what the wiki says and you will be happy.
Use two DRBD volumes like adamb said above which is exactly what the wiki suggests.

The DRBD wiki page has not changed much in many years because it is proven method.

http://pve.proxmox.com/wiki/DRBD

 

[PepeOnaChair]

ok, thank you. I`m just trying to find the best way of my things as always and sometimes I think too much So I`m going to focus to building cluster that way (2 DRBDs) and test it hardly.
best regards
Pep.