[Engine-devel] [vdsm] RFC: New Storage API

Mon Jan 14 22:31:28 UTC 2013

----- Original Message -----
> From: "Ayal Baron" <abaron at redhat.com>
> To: "Saggi Mizrahi" <smizrahi at redhat.com>
> Cc: "engine-devel" <engine-devel at ovirt.org>, "VDSM Project Development" <vdsm-devel at lists.fedorahosted.org>, "Deepak
> C Shetty" <deepakcs at linux.vnet.ibm.com>
> Sent: Monday, January 14, 2013 4:56:05 PM
> Subject: Re: [vdsm] RFC: New Storage API
> 
> 
> 
> ----- Original Message -----
> > 
> > 
> > ----- Original Message -----
> > > From: "Deepak C Shetty" <deepakcs at linux.vnet.ibm.com>
> > > To: "Saggi Mizrahi" <smizrahi at redhat.com>
> > > Cc: "Shu Ming" <shuming at linux.vnet.ibm.com>, "engine-devel"
> > > <engine-devel at ovirt.org>, "VDSM Project Development"
> > > <vdsm-devel at lists.fedorahosted.org>, "Deepak C Shetty"
> > > <deepakcs at linux.vnet.ibm.com>
> > > Sent: Sunday, December 16, 2012 11:40:01 PM
> > > Subject: Re: [vdsm] RFC: New Storage API
> > > 
> > > On 12/08/2012 01:23 AM, Saggi Mizrahi wrote:
> > > >
> > > > ----- Original Message -----
> > > >> From: "Deepak C Shetty" <deepakcs at linux.vnet.ibm.com>
> > > >> To: "Saggi Mizrahi" <smizrahi at redhat.com>
> > > >> Cc: "Shu Ming" <shuming at linux.vnet.ibm.com>, "engine-devel"
> > > >> <engine-devel at ovirt.org>, "VDSM Project Development"
> > > >> <vdsm-devel at lists.fedorahosted.org>, "Deepak C Shetty"
> > > >> <deepakcs at linux.vnet.ibm.com>
> > > >> Sent: Friday, December 7, 2012 12:23:15 AM
> > > >> Subject: Re: [vdsm] RFC: New Storage API
> > > >>
> > > >> On 12/06/2012 10:22 PM, Saggi Mizrahi wrote:
> > > >>> ----- Original Message -----
> > > >>>> From: "Shu Ming" <shuming at linux.vnet.ibm.com>
> > > >>>> To: "Saggi Mizrahi" <smizrahi at redhat.com>
> > > >>>> Cc: "VDSM Project Development"
> > > >>>> <vdsm-devel at lists.fedorahosted.org>, "engine-devel"
> > > >>>> <engine-devel at ovirt.org>
> > > >>>> Sent: Thursday, December 6, 2012 11:02:02 AM
> > > >>>> Subject: Re: [vdsm] RFC: New Storage API
> > > >>>>
> > > >>>> Saggi,
> > > >>>>
> > > >>>> Thanks for sharing your thought and I get some comments
> > > >>>> below.
> > > >>>>
> > > >>>>
> > > >>>> Saggi Mizrahi:
> > > >>>>> I've been throwing a lot of bits out about the new storage
> > > >>>>> API
> > > >>>>> and
> > > >>>>> I think it's time to talk a bit.
> > > >>>>> I will purposefully try and keep implementation details
> > > >>>>> away
> > > >>>>> and
> > > >>>>> concentrate about how the API looks and how you use it.
> > > >>>>>
> > > >>>>> First major change is in terminology, there is no long a
> > > >>>>> storage
> > > >>>>> domain but a storage repository.
> > > >>>>> This change is done because so many things are already
> > > >>>>> called
> > > >>>>> domain in the system and this will make things less
> > > >>>>> confusing
> > > >>>>> for
> > > >>>>> new-commers with a libvirt background.
> > > >>>>>
> > > >>>>> One other changes is that repositories no longer have a
> > > >>>>> UUID.
> > > >>>>> The UUID was only used in the pool members manifest and is
> > > >>>>> no
> > > >>>>> longer needed.
> > > >>>>>
> > > >>>>>
> > > >>>>> connectStorageRepository(repoId, repoFormat,
> > > >>>>> connectionParameters={}):
> > > >>>>> repoId - is a transient name that will be used to refer to
> > > >>>>> the
> > > >>>>> connected domain, it is not persisted and doesn't have to
> > > >>>>> be
> > > >>>>> the
> > > >>>>> same across the cluster.
> > > >>>>> repoFormat - Similar to what used to be type (eg.
> > > >>>>> localfs-1.0,
> > > >>>>> nfs-3.4, clvm-1.2).
> > > >>>>> connectionParameters - This is format specific and will
> > > >>>>> used
> > > >>>>> to
> > > >>>>> tell VDSM how to connect to the repo.
> > > >>>> Where does repoID come from? I think repoID doesn't exist
> > > >>>> before
> > > >>>> connectStorageRepository() return.  Isn't repoID a return
> > > >>>> value
> > > >>>> of
> > > >>>> connectStorageRepository()?
> > > >>> No, repoIDs are no longer part of the domain, they are just a
> > > >>> transient handle.
> > > >>> The user can put whatever it wants there as long as it isn't
> > > >>> already taken by another currently connected domain.
> > > >> So what happens when user mistakenly gives a repoID that is in
> > > >> use
> > > >> before.. there should be something in the return value that
> > > >> specifies
> > > >> the error and/or reason for error so that user can try with a
> > > >> new/diff
> > > >> repoID ?
> > > > Asi I said, connect fails if the repoId is in use ATM.
> > > >>>>> disconnectStorageRepository(self, repoId)
> > > >>>>>
> > > >>>>>
> > > >>>>> In the new API there are only images, some images are
> > > >>>>> mutable
> > > >>>>> and
> > > >>>>> some are not.
> > > >>>>> mutable images are also called VirtualDisks
> > > >>>>> immutable images are also called Snapshots
> > > >>>>>
> > > >>>>> There are no explicit templates, you can create as many
> > > >>>>> images
> > > >>>>> as
> > > >>>>> you want from any snapshot.
> > > >>>>>
> > > >>>>> There are 4 major image operations:
> > > >>>>>
> > > >>>>>
> > > >>>>> createVirtualDisk(targetRepoId, size, baseSnapshotId=None,
> > > >>>>>                      userData={}, options={}):
> > > >>>>>
> > > >>>>> targetRepoId - ID of a connected repo where the disk will
> > > >>>>> be
> > > >>>>> created
> > > >>>>> size - The size of the image you wish to create
> > > >>>>> baseSnapshotId - the ID of the snapshot you want the base
> > > >>>>> the
> > > >>>>> new
> > > >>>>> virtual disk on
> > > >>>>> userData - optional data that will be attached to the new
> > > >>>>> VD,
> > > >>>>> could
> > > >>>>> be anything that the user desires.
> > > >>>>> options - options to modify VDSMs default behavior
> > > >> IIUC, i can use options to do storage offloads ? For eg. I can
> > > >> create
> > > >> a
> > > >> LUN that represents this VD on my storage array based on the
> > > >> 'options'
> > > >> parameter ? Is this the intended way to use 'options' ?
> > > > No, this has nothing to do with offloads.
> > > > If by "offloads" you mean having other VDSM hosts to the heavy
> > > > lifting then this is what the option autoFix=False and the fix
> > > > mechanism is for.
> > > > If you are talking about advanced scsi features (ie. write
> > > > same)
> > > > they will be used automatically whenever possible.
> > > > In any case, how we manage LUNs (if they are even used) is an
> > > > implementation detail.
> > > 
> > > I am a bit more interested in how storage array offloads ( by
> > > that
> > > I
> > > mean, offload VD creation, snapshot, clone etc to the storage
> > > array
> > > when
> > > available/possible) can be done from VDSM ?
> > > In the past there were talks of using libSM to do that. How does
> > > that
> > > strategy play in this new Storage API scenario ? I agree its
> > > implmn
> > > detail, but how & where does that implm sit and how it would be
> > > triggered is not very clear to me. Looking at createVD args, it
> > > sounded
> > > like 'options' seems to be a trigger point for deciding whether
> > > to
> > > use
> > > storage offloads or not, but you spoke otherwise :) Can you
> > > provide
> > > your
> > > vision on how VDSM can understand the storage array capabilities
> > > &
> > > exploit storgae array offloads in this New Storage API context ?
> > > --
> > > Thanks deepak
> > Some will be used automatically whenever possible (storage
> > offloading).
> > Features that favor a specific strategy will be activated when the
> > proper strategy (space, performance) option is selected.
> > In cases when only the user can know whether to use a feature or
> > not
> > we will have options to turn that on.
> > In any case every domain exports a capability list through
> > GetRepositoryCapabilities() that returns a list off repository
> > capabilities.
> > Some capabilities are VDSM specific like CLUSTERED or REQUIRES_SRM.
> > Some are storage capabilities like NATIVE_SNAPSHOTS,
> > NATIVE_THIN_PROVISIONING, SPARSE_VOLUMES, etc...
> > 
> > We are also considering an override mechanism where you can disable
> > features in storage that supports it by setting it in the domain
> > options. This will be done with NO_XXXXX (eg. NO_NATIVE_SNAPSHOTS).
> > This will make the domain not use or expose the capability through
> > the API. I assume it will only be used for testing or in cases
> > where
> > the storage array is known to have problems with a certain feature.
> > Not everything can be disables as an example there is no real way
> > to
> > disable NATIVE_THING_PROVISIONING or SPARSE_VOLUMES.
> 
> Saggi, there are several different discussions going on here which I
> think require some clearing up (and perhaps splitting).
> what I think is missing here:
> 1. distinction of what we believe should be at repo level and what at
> disk level
>     e.g. pre/postZero at repo level, native snapshots as described
>     above would also be repo level (not defined per disk) etc.
No option is inherently repo or disk based (even the ones you mantioned).
It all depends on the VDSM version you are interacting with. I am open to
the suggestion on having a way to query whether certain options are
supported by what operation and in what level dynamically.

As for post-zeroing, currently it is kind of insulting to our users that
we push it as a solution to prevent new VMs from reading old VMs data. It
is just not what it does. It will be replaced with pre-zeroing.

The only reason I see for post zeroing is the "wipe HDD before selling it off"
use case but I don't see how it is valid in virtualized environments especially
with enterprise storage.

> 2. how/where storage offload would work? is there a single
> implementation for repos which detects automatically storage
> capabilities or repo class for each storage type
They will be used automatically if available and supported by VDSM and the
repo format. It doesn't matter to this section of the API whether the user
will have to manually create repositories in specific formats or if it will
be automatic. As it seems, it will probably be automatically.
> 3. and biggest topic is probably - a mapping of the image operations
> and details about the flows (did you send something about that?) -
> i.e. create vdisk flow, copy, etc.
The flows you suggest here are basic flows supported with a single API call.

Because of the nature of image states users need to have a mechanism to
track said image states and make sure fixes are running (if desired)

Everyone is welcome to give it a shot and see how they can implement high
level flows using this API in their own systems. I don't mind helping people
figure it out, just ask.
> 
> 
> 
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