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best practice: one kvm host connected to two nas with one iscsi target each using drbd
Hi all

I need some advice for our setup

We have one kvm node with some virtual machines on. The storage is provided by
two NAS (black box) via iscsi. One of those NAS is for nightly backups. Let's
call that backupNAS and the other one dataNAS. Now I had the idea to duplicate
one dataNAS LU in realtime to the backupNAS (Fall back if dataNAS has an error).
That's how I came across drbd. The LU is used by samba as a network share. Samba
is provided by a VM. The iscsi targets are connected in the kvm host and past on
to the VM as a physical device /dev/vdx and /dev/vdy.

I created a software raid 1 with both LU, but the io was about 30% less than the
io of a single LU. I read that drbd can replicate the data with nearly no loss,
so I wanted to give it a try.

The idea is to use the dataNAS LU as the primary node and the backupNAS LU as
the secondary (protocol A).

I understand
- the setup is not HA
- that usually drbd needs a second (tcp/ip) node to share the data with - but we
don't have a second kvm node (this might change in some time). I have read the
provided howto:
1) Highly Available Virtualization with KVM, ISCSI & Pacemaker
2) Highly Available ISCSI with DRBD and Pacemaker
but both alway use to customizable drbd nodes (I don't know if this is the right
wording). As I said, the NAS are black boxes for me, so I cannot/don't want
install anything on them.

Is there a way to achieve this with my setup?

Thanks for all your help.

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