[vdsm] Storage Device Management in VDSM and oVirt

Deepak C Shetty deepakcs at linux.vnet.ibm.com
Tue Apr 24 11:30:28 UTC 2012

On 04/24/2012 02:07 AM, Ayal Baron wrote:
> ----- Original Message -----
>> On 04/22/2012 12:28 PM, Ayal Baron wrote:
>>>>> This way we'd have a 2 stage process:
>>>>> 1. setupStorage (generic)
>>>> I was looking up on the VDSM archives and there are talks of using
>>>> libstoragemgmt (lsm)
>>> Funny, we started using that acronym for Live Storage Migration :)
>>>> under VDSM. I was wondering if the setupStorage would be something
>>>> where
>>>> lsm would
>>>> be used to do the work, it seems fit for purpose here.
>>> I don't think this is the libstoragemgmt mandate.
>>> libstoragemgmt is:
>>> "A library that will provide a vendor agnostic open source storage
>>> application programming interface (API) for storage arrays."
>>> i.e. it is there to abstract storage array specifics from the user.
>>> It will be used by things like LVM etc, not the other way around.
>>> setupStorage would use libstoragemgmt wherever appropriate of
>>> course.
>>> But as the libstoragemgmt maintainer, Tony (cc'd) can correct me if
>>> I'm wrong here.
>> I was looking at setupStorage as Provisioning + Setting up.
>> I know one of the basic goals of lsm is provision the storage to the
>> host
>> and preparing the storage for consumption is higher layers work.
>> With that, i think then its becomes a 3 stage process, from
>> oVirt/VDSM
>> pov...
>> 1) Provision Storage (using lsm if applicable, based on whether
>> external
>> storage is connected)
>> 2) Setup Storage (prepare the provisioned LUNs for usage)
>> 3) createSD/createGlusterVolume/...  (plugin specific)
>> Since we are talking about Storage management using VDSM, i was
>> interested in understanding the plans, strategy of how VDSM + lsm
>> will integrate ?
> There are various ways of approaching this.
> 1. Given proper storage you could just provision new LUNs whenever you need a new virtual disk and utilize storage side thin provisioning and snapshots for most of your needs.
> When you have such storage you don't really need steps 2 and 3 above.  Your storage is your virtual images repository.
> Although quite simple and powerful, very few arrays are capable of growing to a very large number of objects (luns + snapshots + whatever) today, so I don't see this being the most common use case any time soon.

This is not clear to me. This only talks about provisioning but not consuming.
2 and 3 above are required from a consumability perspective. The LUNs will have
to prepared and used by LVM (pv, vg, lv, metadata) for VDSM to host a storage domain.

> 2. Provision LUNs (either statically or dynamically using lsm) once, preferably thinly provisioned. Then setupStorage (storage domain over VG / gLuster / other) and use lsm for creating snapshots/clones on the fly
> In my opinion this will be more prevalent to begin with.
> With lsm we will (hopefully) have a way of enumerating storage side capabilities so then when we create a repository (gluster / sd / ...) we'd be able to determine on the fly what capabilities it has and determine if to use these or to use virtualized capabilities (e.g. in the virt case when you need to create a snapshot use qcowX).
> In oVirt, once you've defined a storage domain and it exposes a set of capabilities, user should be able to override (e.g. even though storage supports snapshots, I want to use qcow as this storage can only create 255 snapshots per volume and I need more than that).
> I'm assuming that we will not have any way of knowing the limits per machine.
> Does that make sense?

Agree to #2. Thinking deeper....

1) Provisioning Storage

Provisioning storage using lsm would require new VDSM verbs to be added,
which can create / show the LUNs to the oVirt user and user can then
select which LUN(s) to use for setupStorage.

Provisioning LUNs will probably exploit the lsm capabilities and provide
the options to the user to create the LUNs using the available array

With GlusterFS also providing some of the array capabilities (stripe,
replicate etc), user might want to provision GlusterFS volume (with
whatever capabilities gluster offers) to host storage upon, especially
if the storage is coming from not-so-reliable commodity hw storage.

I feel this also has to be considered as part of provisioning and should
come before the setupStorage step.

IMHO, there should be a "Storage Provisioning" tab in oVirt which will
allow user to ...

     1a) Carve LUNs from external Storage array.

     1b) Provision storage as GlusterFS volume. User can select the LUNs
carved (from #1a) as bricks for GlusterFS volume, if need be.

     1c) Use local host free disk space.

Somewhere here there should be option ( as applicable) for user to
select whether to exploit storage array features or host virt
capabilities for say snapshot, in cases where both are applicable.

2) Setup Storage

Here the user would create VDSM file or block based storage domain,
based on the storage provisioned from the "Storage Provisioning" tab.
I believe this is where  VDSM will add its metadata to the provisioned
storage to make it a storage domain.

IMHO for image operations like snapshot/clone, VDSM will have to track&
maintain whether the image is served by local host, external storage
array or gluster volume and accordingly use the lvm, lsm or gluster apis
to get the job done.

3) Not sure if anymore steps needed ?


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