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

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 well.

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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