First of all I'd like to suggest not using the LSM acronym as it can also mean 
live-storage-migration and maybe other things.

Secondly I would like to avoid talking about what needs to be changed in VDSM 
before we figure out what exactly we want to accomplish.

Also, there is no mention on credentials in any part of the process.
How does VDSM or the host get access to actually modify the storage array?
Who holds the creds for that and how?
How does the user set this up?

In the array as domain case. How are the luns being mapped to initiators. What 
about setting discovery credentials.
In the array set up case. How will the hosts be represented in regards to 
How will the different schemes and capabilities in regard to authentication 
methods will be expressed.

Rest of the comments inline

----- Original Message -----
> From: "Deepak C Shetty" <>
> To: "VDSM Project Development" <>
> Cc:,
> Sent: Wednesday, May 30, 2012 5:38:46 AM
> Subject: [Engine-devel] RFC: Writeup on VDSM-libstoragemgmt integration
> 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.
> thanx,
> deepak
> [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:
> 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
> 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 @,192
> Current plan is to have LSM co-exist with VDSM on the virtualization
> nodes.
> *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.
[SM] What about the clustered case, The management or the mailbox will have to 
be involved. Pros\Cons? Is there a capability for the storage to announce a 
change in topology? Can libstoragemgmt consume it? Does it even make sense?
> 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.
[SM] This is all a bit vague in my opinion, concrete cases might prove more 
> 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
> 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
> 2. create a LUN for a new storage domain

[SM] Maybe the engine should do the work? What about permission? Will all hosts 
have the credentials to mess with the storage? Will they be passed on a per 
call basis to prevent other users from having access to the storage?
> 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
I find this hard to understand. Maybe a different notation?
In ant case there is an abstracted case ie. storage domain. And there is a 
direct case ie. user provision luns to be used by VDSM and others as well.
The will both have different ways of representing the same underlying objects.
Also, I think that credentials might be tricky to represent as different arrays 
use different schemes to allocated users\hosts to luns\targets.
> ?
> 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 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.
> _______________________________________________
> Engine-devel mailing list
vdsm-devel mailing list

Reply via email to