[vdsm] Storage Device Management in VDSM and oVirt

[Deepak C Shetty]

>> This seems interesting.
>>
>> I am interested in pursuing this further and helping contribute to
>> the
>> vdsm lsm integration. lsm is still in the early stages, but i feel
>> its
>> the right time to start influencing it so that vdsm integration can
>> be
>> smooth. My interest mainly lies in how external storage array can be
>> integrated into oVirt/VDSM and help oVirt exploit the array offload
>> features as part of the virtualization stack.
>>
>> I didn't find any oVirt wiki page on this topic, tho' there is a old
>> mailing list thread on vdsm lsm integration, which when read brings
>> up
>> more issues to discuss :)
>> How does storage repo engine and possible vdsm services framework ( i
>> learnt about these in my brief chat with Saggie some time back) play
>> a
>> role here ?
> Maybe Saggi could elaborate here.
>
>> Can "Provisioning Storage" itself be like a high level service, with
>> gluster and lsm  exposing storage services, which vdsm can enumerate
>> and
>> send to oVirt GUI, is that the idea ?
> I'm not sure "Provisioning Storage" is a clear enough definition, as it could cover a lot of possibly unrelated things, but I'd need to understand more what you mean to really be able to comment properly.
>

Well, I was envisioning oVirt as being able to provision and consume 
storage, both, going ahead.
Provisioning thru' vdsm-libstoragemgmt (lsm) integration. oVirt user 
should be able to carve out LUNs,
be able to associate the LUNs visibility to host(s) of a oVirt cluster, 
all via libstoragemgmt interfaces.

With gluster being integrated into vdsm, oVirt user can provision and 
manage gluster volumes soon,
which also falls under "provisioning storage", hence I was wondering if 
there would be a new tab
in oVirt for "provisioning storage", where gluster ( in near future) and 
external array/LUNs  ( via
vdsm -lsm integration) can be provisioned.


>> Is there any wiki page on this topic which lists the todos on this
>> front, which I can start looking at ?
> Unfortunately there is not as we haven't sat down to plan it in depth, but you're more than welcome to start it.
>
> Generally, the idea is as follows:
> Currently vdsm has storage virtualization capabilites, i.e. we've implemented a form of thin-provisioning, we provide snapshots using qcow etc, without relying on the hardware.  Using lsm we could have feature negotiation and whenever we can offload, do it.
> e.g. we could know if a storage array supports thin cloning, if it supports thick cloning, if a LUN supports thin provisioning etc.
> In the last example (thin provisioning) when we create a VG on top of a thin-p LUN we should create all disk image (LVs) 'preallocated' and avoid vdsm's thin provisioning implementation (as it is not needed).
>

I was thinking libstoragemgmt 'query capability' or similar interface 
should help vdsm know the array capabilities.
I agree that if the backing LUN already is thinp'ed, then vdsm should 
not add its own over it. So such usecases & needs
from vdsm perspective need to be thought about and eventually it should 
influence the libstoragemgmt interfaces

> However, we'd need a mechanism at domain level to 'disable' some of the capabilities, so for example if we know that on a specific array snapshots are limited or provide poor performance (worse than qcow) or whatever, we'd be able to fall back to vdsm's software implementation.
>

I was thinking that its for the user to decide, not sure if we can 
auto-detect and automate this. But i feel this falls under the 'advanced 
usecase' category :)
We can always think about this later, rite ?