[Users] convert thin provisioned disks to preallocated

[Omer Frenkel]

----- Original Message -----

> From: "Alan Johnson" <alan at datdec.com>
> To: "users" <users at ovirt.org>
> Sent: Wednesday, September 18, 2013 3:47:08 AM
> Subject: [Users] convert thin provisioned disks to preallocated

> I am pretty sure I know the answer, but is there any way to do this
> gracefully, i.e. within the confines of the oVirt API? This is on an iSCSI
> storage domain. My understanding and further research suggest no, but I
> wanted to ask before we endeavor on a major overhaul of a production system
> that some one setup without knowing the better of to the 2 for such use.

> I am very familiar with the underlying systems (LVM, KVM, etc.) and would
> appreciate any suggested hacks. So far, here is what I have come up with:

> Sure to work: Setup a new VM with preallocated drives. Boot both VMs off of a
> live virtual CD. Use cat/pv and nc (netcat) to read directly from the block
> devices on one and write directly to the block devices on the other. Reboot
> the new VM from the internal disks. Tweak MAC addresses along the way so the
> new VM gets those of the old. The down side is the down time, but we can
> probably swallow it if we have to. Any other risks?

> Might work: Create a new VM. Identify the logical volumes (LVs) are assigned
> for that block devices used by the new and the old. Log into the SPM and
> read directly from the old LVs to the new. This is similar to that above,
> but I expect I need to run the data through some kind of qcow2-to-raw
> conversion process to make this work. Similar down sides to the above, but
> maybe less so? Thoughts?

> Another thought I had was to just write zeros to the empty space on the block
> devices, from inside the guest OS, until the full allocation is achieved.
> The down side is potential impact on performance of the system while it is
> filling up and for the (hopefully) very short time the file system is full
> before an rm of the zeros file kicks in. Also we would still have qcow2
> underneath, so would it still add overhead, or does that only apply when it
> grows? Any other down sides to this?

> Thanks in advance for your thoughts and consideration.

i guess that using ovirt api you can export the vm, and import back changing the allocation policy of the disks.. 
need to verify this though. 

> ________________
> Alan Johnson
> alan at datdec.com
> Date Format PSA

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