On 06/18/2012 09:26 PM, Shu Ming wrote:
On 2012-5-30 17:38, Deepak C Shetty wrote:
Hello All,

    I have a draft write-up on the VDSM-libstoragemgmt integration.
I wanted to run this thru' the mailing list(s) to help tune and crystallize it, before putting it on the ovirt wiki. I have run this once thru Ayal and Tony, so have some of their comments incorporated.

I still have few doubts/questions, which I have posted below with lines ending with '?'

Comments / Suggestions are welcome & appreciated.


[Ccing engine-devel and libstoragemgmt lists as this stuff is relevant to them too]


1) Background:

VDSM provides high level API for node virtualization management. It acts in response to the requests sent by oVirt Engine, which uses VDSM to do all node virtualization related tasks, including but not limited to storage management.

libstoragemgmt aims to provide vendor agnostic API for managing external storage array. It should help system administrators utilizing open source solutions have a way to programmatically manage their storage hardware in a vendor neutral way. It also aims to facilitate management automation, ease of use and take advantage of storage vendor supported features which improve storage performance and space utilization.

Home Page: http://sourceforge.net/apps/trac/libstoragemgmt/

libstoragemgmt (LSM) today supports C and python plugins for talking to external storage array using SMI-S as well as native interfaces (eg: netapp plugin ) Plan is to grow the SMI-S interface as needed over time and add more vendor specific plugins for exploiting features not possible via SMI-S or have better alternatives than using SMI-S. For eg: Many of the copy offload features require to use vendor specific commands, which justifies the need for a vendor specific plugin.

2) Goals:

2a) Ability to plugin external storage array into oVirt/VDSM virtualization stack, in a vendor neutral way.

2b) Ability to list features/capabilities and other statistical info of the array

2c) Ability to utilize the storage array offload capabilities from oVirt/VDSM.

3) Details:

LSM will sit as a new repository engine in VDSM.
VDSM Repository Engine WIP @ http://gerrit.ovirt.org/#change,192

Current plan is to have LSM co-exist with VDSM on the virtualization nodes.

Does that mean LSM will be a different daemon process than VDSM? Also, how about the vendor's plugin, another process in the nodes?

Pls see the LSM homepage on sourceforge.net on how LSM works. It already has a lsmd ( daemon) which invokes the appropriate plugin based on the URI prefix. vendor plugins in LSM are supported in LSM as a .py module, which is invoked based on the URI prefix, which will be vendor specific. See the netapp vendor plugin.py in LSM source.

*Note : 'storage' used below is generic. It can be a file/nfs-export for NAS targets and LUN/logical-drive for SAN targets.

VDSM can use LSM and do the following...
    - Provision storage
    - Consume storage

3.1) Provisioning Storage using LSM

Typically this will be done by a Storage administrator.

oVirt/VDSM should provide storage admin the
- ability to list the different storage arrays along with their types (NAS/SAN), capabilities, free/used space. - ability to provision storage using any of the array capabilities (eg: thin provisioned lun or new NFS export ) - ability to manage the provisioned storage (eg: resize/delete storage)

Once the storage is provisioned by the storage admin, VDSM will have to refresh the host(s) for them to be able to see the newly provisioned storage.

3.1.1) Potential flows:

Mgmt -> vdsm -> lsm: create LUN + LUN Mapping / Zoning / whatever is needed to make LUN available to list of hosts passed by mgmt
Mgmt -> vdsm: getDeviceList (refreshes host and gets list of devices)
Repeat above for all relevant hosts (depending on list passed earlier, mostly relevant when extending an existing VG)
Mgmt -> use LUN in normal flows.

3.1.2) How oVirt Engine will know which LSM to use ?

Normally the way this works today is that user can choose the host to use (default today is SPM), however there are a few flows where mgmt will know which host to use: 1. extend storage domain (add LUN to existing VG) - Use SPM and make sure *all* hosts that need access to this SD can see the new LUN 2. attach new LUN to a VM which is pinned to a specific host - use this host 3. attach new LUN to a VM which is not pinned - use a host from the cluster the VM belongs to and make sure all nodes in cluster can see the new LUN

So this model depend on the work of removing storage pool?

I am not sure and want the experts to comment here. I am not very clear yet on how things will work post SPM is gone. Here its assumed SPM is present.

Flows for which there is no clear candidate (Maybe we can use the SPM host itself which is the default ?)
1. create a new disk without attaching it to any VM

So the new floating disk should be exported to all nodes and all VMs?

2. create a LUN for a new storage domain

3.2) Consuming storage using LSM

Typically this will be done by a virtualization administrator

oVirt/VDSM should allow virtualization admin to
    - Create a new storage domain using the storage on the array.
- Be able to specify whether VDSM should use the storage offload capability (default) or override it to use its own internal logic.

4) VDSM potential changes:

4.1) How to represent a VM disk, 1 LUN = 1 VMdisk or 1 LV = 1 VMdisk ? which bring another question...1 array == 1 storage domain OR 1 LUN/nfs-export on the array == 1 storage domain ?

Pros & Cons of each...

1 array == 1 storage domain
    - Each new vmdisk (aka volume) will be a new lun/file on the array.
- Easier to exploit offload capabilities, as they are available at the LUN/File granularity - Will there be any issues where there will be too many LUNs/Files ... any maxluns limit on linux hosts that we might hit ?
        -- VDSM has been tested with 1K LUNs and it worked fine - ayal
- Storage array limitations on the number of LUNs can be a downside here. - Would it be ok to share the array for hosting another storage domain if need be ? -- Provided the existing domain is not utilising all of the free space
        -- We can create new LUNs and hand it over to anyone needed ?
-- Changes needed in VDSM to work with raw LUNs, today it only has support for consuming LUNs via VG/LV.

1 LUN/nfs-export on the array == 1 storage domain
- How to represent a new vmdisk (aka vdsm volume) if its a LUN provisioned using SAN target ?
        -- Will it be VG/LV as is done today for block domains ?
-- If yes, then it will be difficult to exploit offload capabilities, as they are at LUN level, not at LV level. - Each new vmdisk will be a new file on the nfs-export, assuming offload capability is available at the file level, so this should work for NAS targets ?
    - Can use the storage array for hosting multiple storage domains.
-- Provision one more LUN and use it for another storage domain if need be. - VDSM already supports this today, as part of block storage domains for LUNs case.

Note that we will allow user to do either one of the two options above, depending on need.

4.2) Storage domain metadata will also include the features/capabilities of the storage array as reported by LSM. - Capabilities (taken via LSM) will be stored in the domain metadata during storage domain create flow. - Need changes in oVirt engine as well ( see 'oVirt Engine potential changes' section below )

4.3) VDSM to poll LSM for array capabilities on a regular basis ?
Per ayal:
- If we have a 'storage array' entity in oVirt Engine (see 'oVirt Engine potential changes' section below ) then we can have a 'refresh capabilities' button/verb.
    - We can periodically query the storage array.
- Query LSM before running operations (sounds redundant to me, but if it's cheap enough it could be simplest).

Probably need a combination of 1+2 (query at very low frequency - 1/hour or 1/day + refresh button)

5) oVirt Engine potential changes - as described by ayal :

- We will either need a new 'storage array' entity in engine to keep credentials, or, in case of storage array as storage domain, just keep this info as part of the domain at engine level. - Have a 'storage array' entity in oVirt Engine to support 'refresh capabilities' as a button/verb. - When user during storage provisioning, selects a LUN exported from a storage array (via LSM), the oVirt Engine would know from then onwards that this LUN is being served via LSM. It would then be able to query the capabilities of the LUN and show it to the virt admin during storage consumption flow.

6) Potential flows:
    - Create snapshot flow
-- VDSM will check the snapshot offload capability in the domain metadata -- If available, and override is not configured, it will use LSM to offload LUN/File snapshot

If a LSM try to snapshot a running volume, does that mean all the IO activity to the volume will be blocked when the snapshot is undergoing?

If VDSM offloads the snapshot to the array ( via LSM) the array will take care of the snapshotting.... typically i believe it will quiese the I/O temporarily for few ms ? and take a point-in-time copy of the LUN/File and resume the I/O... i think it will happen transparent to the vdsm/host.

-- If override is configured or capability is not available, it will use its internal logic to create
           snapshot (qcow2).

    - Copy/Clone vmdisk flow
-- VDSM will check the copy offload capability in the domain metadata -- If available, and override is not configured, it will use LSM to offload LUN/File copy -- If override is configured or capability is not available, it will use its internal logic to create
           snapshot (eg: dd cmd in case of LUN).

7) LSM potential changes:

- list features/capabilities of the array. Eg: copy offload, thin prov. etc.
    - list containers (aka pools) (present in LSM today)
- Ability to list different types of arrays being managed, their capabilities and used/free space - Ability to create/list/delete/resize volumes ( LUN or exports, available in LSM as of today) - Get monitoring info with object (LUN/snapshot/volume) as optional parameter for specific info. eg: container/pool free/used space, raid type etc.

Need to make sure above info is listed in a coherent way across arrays (number of LUNs, raid type used? free/total per container/pool, per LUN?. Also need I/O statistics wherever possible.

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