[ovirt-users] Local and Shared storage in same datacenter

Yaniv Kaul ykaul at redhat.com
Sun Oct 30 10:35:21 UTC 2016

On Sun, Oct 30, 2016 at 12:02 PM, Mike (maillinglists) <maillist at probie.nl>

> Hi guys,
> There have been a few related questions already that I could find, but I
> did not find anything relating to my specific use case.
> Currently it is not possible to mix local storage with shared storage in
> the same datacenter.
> The reason seems to be because of the storage pool manager (SPM).
> This is a role in the datacenter provided to one specific host.
> While I understand that this makes having local storage impossible, I
> believe there is a use case to have local storage in a shared storage
> datacenter.

Indeed, this is one of the more appealing use cases. There are others s

> Consider the following:
> I have a few applications that require 1 milli second latency and at most
> 2 milli second.

For read, write or both?

> That is not consistenly achievable with shared storage, to that end I
> added flash storage to a few hypervisors.

You could have flash on your shared storage.

> About 5% of my servers require this and are not that resource hungry to
> require a dedicated physical server.
> That same 5% also has no requirement to be migrated if a host fails.
> So in short I have 5 heavy hosts running ovirt with a shared storage
> domain on NFS for 95% of my servers.
> All running fine, but I am now unable to run my remaining 5%.

Perhaps, if there are no HA requirements, those VMs with local domain needs
can be in their own DC, a local one? If it's just 5%, shouldn't be much of
an effort?

> To finish up my summary I have been testing various virtualization
> technologies, like VmWare and Hyper-V.
> They allow such configurations as I mentioned.
> I already had some chat on irc with various guys and they suggested that I
> put this on the mailing list, so here goes.
> My suggestion would be to evoluate from SPM to SDM.

Easier said than done... We have worked on this for quite some time, it's
not as easy as one might think.

> SDM stands for Storage Domain Manager.
> This would create the possibility to have all nodes in the datacenter
> participate in the storage handling.
> A extra benefit would be that local storage could be added.
> What do you think?

There are other use cases we think flash on the host can be used, some may
be of use for your use case.
For example, dm-cache[1].

We are still looking at this. I think Gluster already can make use it for
cache, for example.

[1] https://people.redhat.com/mskinner/rhug/q1.2016/dm-cache.pdf

> Thanks for reading.
> Kind regards,
> Mike van Goor
> _______________________________________________
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> Users at ovirt.org
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