[DRBD-user] DRBD + ZFS

[David Bruzos]

Hello folks,
    I've used DRBD over ZFS for many years and my experience has been very possitive.  My primary use case has been virtual machine backing storage for Xen hypervisors, with dom0 running ZFS and DRBD.  The realtime nature of DRBD replication allows for VM migrations, etc, and ZFS makes remote incremental backups awesome.  Overall, it is a combination that is hard to beat.

* Key things to keep in mind:

    . The performance of DRBD on ZFS is not the best in the world, but the benefits of a properly configured and used setup far outweigh the performance costs.
    . If you are not limited buy storage size (typical when using rotating disks), I would absolutely recommend mirror vdevs with ashift=12 for best results in most circumstances.
    . If space is a limiting factor (typical with SSD/NVME), I use raidz, but careful considerations have to be made, so you don't end up wasting tuns of space, because of ashift/blocksize/striping issues.
    . Compression works great under the DRBD devices, but volblocksize/ashift details are extremely important to get the most out of it.
    . I would not create additional ZFS file systems on top of the DRBD devices for compression or any other intensive feature, just not worth it, you want that as close to the physical storage as possible.

    I do run a few ZFS file systems on virtual machines that are backed by DRBD devices on top of ZFS, but I am after other ZFS features in those cases.  The VMs running ZFS have compression=off, no vdev redundancy, optimized volblocksize for the situation/workload in question, etc.  My typical goto filesystem for VMs is XFS, because it is lean-and-mean and has the kind of features that everyone should want in a general purpose FS.

If you have specific questions, let me know.

David

-- 
David Bruzos (Systems Administrator)
Jacksonville Port Authority
2831 Talleyrand Ave.
Jacksonville, FL  32206
Cell: (904) 625-0969
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Email: david.bruzos at jaxport.com

On Fri, Aug 20, 2021 at 11:32:31AM +0000, Eric Robinson wrote:
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> My main motivation is the desire for a compressed filesystem. I have experimented with using VDO for that purpose and it works, but the setup is complex and I don’t know if I trust it to work well when VDO is in a stack of Pacemaker cluster resources. If there a better way of getting compression to work above DRBD?
> 
> -Eric
> 
> 
> From: rabin at isoc.org.il <rabin at isoc.org.il>
> Sent: Thursday, August 19, 2021 4:43 PM
> To: Eric Robinson <eric.robinson at psmnv.com>
> Cc: drbd-user at lists.linbit.com
> Subject: Re: [DRBD-user] DRBD + ZFS
> 
> Not sure ZFS is the right choice as an underline for a resource,
> it is powerful but also complex (as a code base), which will probably will make it slow.
> 
> unless you are going to expose the ZVOL or the dataset directly to be consumed,
> stacking ZFS over DRBD over ZFS, seems to me as a bad idea.
> 
> 
> 
> Rabin
> 
> 
> On Wed, 18 Aug 2021 at 09:37, Eric Robinson <eric.robinson at psmnv.com<mailto:eric.robinson at psmnv.com>> wrote:
> I’m considering deploying DRBD between ZFS layers. The lowest layer RAIDZ will serve as the DRBD backing device. Then I would build another ZFS filesystem on top to benefit from compression. Any thoughs, experiences, opinions, positive or negative?
> 
> --Eric
> 
> 
> 
> 
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