[DRBD-user] DRBD + ZFS
David Bruzos
david.bruzos at jaxport.com
Tue Aug 24 21:03:00 CEST 2021
Hello Eric:
> What degree of performance degradation have you observed with DRBD over ZFS? Our servers will be using NVME drives with 25Gbit networking:
Unfortunately, I have not had the time to properly benchmark and compare a setup like yours with DRBD on top of ZFS. Very superficial tests show that my I/O is more than sufficient for my workload, so I'm then more interested is the data integrity, snapshotting, compression, etc. I would not want to create misinformation by sharing I/O stats that are not taking into account the many aspects of a proper ZFS benchmark and that are not being compared against an alternative setup.
In the days of spinning rust storage, I always used mirrored vdevs, always added a fast ZIL, lots of RAM for ARC and a couple of caching devices for L2ARC, so the performance was great when compared with the alternatives.
> Since you don't recommend having ZFS above DRBD, what filesystem do you use over DRBD?
I've always had good results with XFS on LVM (very thin). That combination usually gives you good flexibility at the VM level and the performance is great. These days, ext4 is a reasonable choice, but I still use XFS most of the time.
I would like to see what other folks think about the XFS+LVM combination for VMs vs something like ext4+LVM.
> Linbit recommends that compression take place above DRBD rather than below. What are your thoughts about their recommendation versus your approach?
If you can provide a link to their recommendation, I can be more specific. In any case, I'm sure their recommendation is reasonable depending on what your specific workload is. In my case, I mostly use compression at the backing storage level, because it gives me a predictable and well understood VM environment where I can run a wide variety of guest operating systems, applications, workloads, etc, without having to worry about the specifics for each possible VM scenario.
The reason I normally don't use ZFS for VMs is because I believe it best serves its purpose at the backing storage level for many reasons. ZFS is designed to leverage lots of RAM for ARC, to handle the storage directly, to do many things with your hardware that are very much abstracted away at the guest level.
What is your specific usage scenario?
--
David Bruzos (Systems Administrator)
Jacksonville Port Authority
2831 Talleyrand Ave.
Jacksonville, FL 32206
Cell: (904) 625-0969
Office: (904) 357-3069
Email: david.bruzos at jaxport.com
On Tue, Aug 24, 2021 at 03:21:10PM +0000, Eric Robinson wrote:
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>
> Hi David --
>
> Thanks for your feedback! I do have a couple of follow-up questions/comments.
>
> What degree of performance degradation have you observed with DRBD over ZFS? Our servers will be using NVME drives with 25Gbit networking.
> Since you don't recommend having ZFS above DRBD, what filesystem do you use over DRBD?
> Linbit recommends that compression take place above DRBD rather than below. What are your thoughts about their recommendation versus your approach?
>
> --Eric
>
>
>
>
> > -----Original Message-----
> > From: David Bruzos <david.bruzos at jaxport.com>
> > Sent: Saturday, August 21, 2021 8:34 AM
> > To: Eric Robinson <eric.robinson at psmnv.com>
> > Cc: rabin at isoc.org.il; drbd-user at lists.linbit.com
> > Subject: Re: [DRBD-user] DRBD + ZFS
> >
> > 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
> > Office: (904) 357-3069
> > Email: david.bruzos at jaxport.com
> >
> > On Fri, Aug 20, 2021 at 11:32:31AM +0000, Eric Robinson wrote:
> > > EXTERNAL
> > > This message is from an external sender.
> > > Please use caution when opening attachments, clicking links, and
> > responding.
> > > If in doubt, contact the person or the helpdesk by phone.
> > > ________________________________
> > >
> > > 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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