[DRBD-user] DRBD over ZFS - or the other way around?

Veit Wahlich cru.lists at zodia.de
Fri Aug 18 17:22:26 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.

Am Freitag, den 18.08.2017, 15:46 +0200 schrieb Gionatan Danti:
> Il 18-08-2017 14:40 Veit Wahlich ha scritto:
> > VM live migration requires primary/primary configuration of the DRBD
> > ressource accessed by the VM, but only during migration. The ressource
> > can be reconfigured for allow-two-primaries and revert this setting
> > afterwards on the fly.
> Hi Veit, this is interesting.
> So you suggest to use DRBD on top of a ZVOLs?

Yes, I regard qemu -> DRBD -> volume management [-> RAID] -> disk the
most recommendable solution for this scenario.

I personally go with LVM thinp for volume management, but ZVOLs should
do the trick, too. 

With named ressources (named after VMs) and multiple volumes per
ressource (for multiple VM disks), this works very well for us for
hundreds of VMs.

Having a cluster-wide unified system for numbering VMs is very
advisable, as it allows to calculate the ports and minor numbers for
both DRBD and KVM/qemu configuration.

* numbering VMs from 0 to 999 as <num>, padded with leading zeros
* numbering volumes from 0 to 99 as <vol>, padded with leading zeros
* DRBD ressource port: 10<num>
* VNC/SPICE unencrypted port: 11<num>
* SPICE TLS port: 12<num>
* DRBD minor: <num><volume>

Let's say your VM gets number 123, it has 3 virtual disks and uses VNC:
* DRBD ressource port: 10123
* VNC port: 11123
* DRBD minor of volume/VM disk 0: 12300
* DRBD minor of volume/VM disk 1: 12301
* DRBD minor of volume/VM disk 2: 12302

Best regards,
// Veit

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