On Sun, Nov 26, 2017 at 12:25 PM, Shani Leviim <sleviim@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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