[DRBD-user] Hardware specs & upgrades

[Vito Botta]

Wonderful, it doesn't sound too bad then, I will be using three nodes with
Kubernetes. Thanks!

On Fri, 9 Aug 2019, 13.45 Roland Kammerer, <roland.kammerer at linbit.com>
wrote:

> On Thu, Aug 08, 2019 at 10:41:37PM +0300, Vito Botta wrote:
> > Hi,
> >
> > at the moment I am testing with 3 nodes that have 4 cores and 16 GB of
> > ram, and all works great. However since DRBD/Linstor have very little
> > overhead compared to other storage products I've tried with
> > Kubernetes, I was wondering whether 2 cores and 8 GB of ram would be
> > sufficient?
>
> LINSTOR/DRBD are not that resource hungry. Java is a but, but Rene got
> some pretty nice results with some minimal configurations. Rene?
>
> > Also, if I have three servers with volumes being replicated, how can I
> > avoid downtime when upgrading whenever a new release is out?
>
> That depends a bit what you want to update:
>
> The really nice thing about DRBD and LINSTOR are that the control plane
> is separated from the data plane. Which means you shut down LINSTOR
> completely and your data is still up, because DRBD continues to
> replicate data. So updating LINSTOR is easy, just do it :)
>
> If you need to update DRBD (i.e., the kernel modules), then you
> basically do this:
> - move all resources away from the node you want to update (i.e, no DRBD
>   resource is Primary anymore)
> - drbdadm down all
> - rmmod
> - upgrade
>
> And this then you do the same for the next node. We are very careful
> that you can have mixed DRBD version until you finally upgraded your
> last storage node. Obviously you need to have at least 2 storage nodes,
> if you only have one diskful and one diskless node, then yeah, you will
> have downtime. And maybe you want to first provide "over redundancy" via
> an additional diskful replica, or you are fine that your N times
> redundant resource is only N-1 during you upgrade your storage. But that
> all depends on your use case.
>
> The important thing is that data and control plane.
>
> Best, rck
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