[ovirt-users] Shared vs Local Storage for Datacenters

[Yedidyah Bar David]

On Sun, Nov 26, 2017 at 12:25 PM, Shani Leviim <sleviim at redhat.com> wrote:
> Hi,
>
>> I'm wondering at the moment what the actual difference is between
>> Shared and Local Storage Datacenters.
>>
> By definition, taken from here [1],
> Local storage:
> When you set up a host to use local storage, the host automatically gets
> added to a new data center and cluster that no other hosts can be added to.
> Multiple host clusters require that all hosts have access to all storage
> domains, which is not possible with local storage.
> Virtual machines created in a single host cluster cannot be migrated, fenced
> or scheduled.
>
> Shared storage:
> Set up NFS shares that will serve as a data domain and an export domain.
> Storage data domains can be unattached from a data center and imported to
> another data center in the same environment, or in a different environment.
> Virtual machines, floating virtual disk images, and templates can then be
> uploaded from the imported storage domain to the attached data center.
>
>>
>> As far as I can see a Local DC supports NFS as well which makes it a
>> more flexible DC in storage if you ask me, so why do both still exist
>> ?
>>
> In fact by setting a local DC, only one host can be added and there's no
> high availability functionality.
> According to [2], a local DC supports NFS shares for migration needs.
> In case of sharing resources between more that one host, you should use a
> Shared DC.
>
>>
>> Is it possible in a decent way to change a running Shared Storage DC
>> to a Local one and Keep the NFS shares and add some local mounts for
>> specific hosts ?
>>
> Since a shared DC can support more than one host (while local DC supports
> exactly one), it's not possible moving from 'Share' type to a 'Local' type.

Depending on your specific needs, you might want to keep using shared
storage and use a vdsm hook to attach a local disk. See also:

https://github.com/oVirt/vdsm/tree/master/vdsm_hooks

Check specifically localdisk, vmdisk, scratchpad.

>
>>
>> I hope someone can clearify!
>
> Hope it makes more sense.
>
>
> [1] https://www.ovirt.org/documentation/admin-guide/chap-Storage/
> [2] https://bugzilla.redhat.com/show_bug.cgi?id=1302185
>
> Regards,
> Shani Leviim
>
>
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-- 
Didi