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

[Mike (maillinglists)]

Hi Yaniv,

Op 30-10-2016 om 11:35 schreef Yaniv Kaul:
>
>
> On Sun, Oct 30, 2016 at 12:02 PM, Mike (maillinglists)
> <maillist at probie.nl <mailto:maillist at 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?
Both I'm afraid.
>
>
>     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.
The problem with shared flash storage is the storage network required in 
between. I have seen shared NFS storage at 1ms latency, but that has not 
been stable and this application requires stable 1ms latencies.
>
>
>     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?
Can a host be in 2 datacenters?
I was not aware of this and I will investigate.
>
>
>     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.
I appreciate your honousty, but still hope this can be achieved.
>
>
>     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.
> Y.
Gluster is an angle we are investigating, but takes time to look into. 
Thanks!
>
> [1] https://people.redhat.com/mskinner/rhug/q1.2016/dm-cache.pdf
Thanks!
>
>
>
>     Thanks for reading.
>
>     Kind regards,
>     Mike van Goor
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