On 12/04/2012 03:52 PM, Saggi Mizrahi wrote:
> 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.
> 
> 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
> 
> returns the id of the new VD

I'm guessing there will be a way to find out how much space is available
for a specified repo before you try to create a virtual disk on it?

> 
> createSnapshot(targetRepoId, baseVirtualDiskId,
>                userData={}, options={}):
> targetRepoId - The ID of a connected repo where the new sanpshot will be 
> created and the original image exists as well.
> size - The size of the image you wish to create
> baseVirtualDisk - the ID of a mutable image (Virtual Disk) you want to 
> snapshot
> userData - optional data that will be attached to the new Snapshot, could be 
> anything that the user desires.
> options - options to modify VDSMs default behavior
> 
> returns the id of the new Snapshot
> 
> copyImage(targetRepoId, imageId, baseImageId=None, userData={}, options={})
> targetRepoId - The ID of a connected repo where the new image will be created
> imageId - The image you wish to copy
> baseImageId - if specified, the new image will contain only the diff between 
> image and Id.
>               If None the new image will contain all the bits of image Id. 
> This can be used to copy partial parts of images for export.
> userData - optional data that will be attached to the new image, could be 
> anything that the user desires.
> options - options to modify VDSMs default behavior
> 
> return the Id of the new image. In case of copying an immutable image the ID 
> will be identical to the original image as they contain the same data. 
> However the user should not assume that and always use the value returned 
> from the method.

Can the target repo id be itself?  The case where a user wants to make a
copy of a virtual disk in the same repo.  A caller could snapshot the
virtual disk and then create a virtual disk from the snapshot, but if
the target repo could be the same as source repo then they could use
this call as long as the returned ID was different.

Does imageId IO need to be quiesced before calling this or will that be
handled in the implementation (eg. snapshot first)?

> removeImage(repositoryId, imageId, options={}):
> repositoryId - The ID of a connected repo where the image to delete resides
> imageId - The id of the image you wish to delete.
>

What is the behavior if you delete snapshots or virtual disks that have
dependencies on one another?  For example, delete the snapshot a virtual
disk is based on or delete the virtual disk a snapshot is based on?

> 
> ----
> getImageStatus(repositoryId, imageId)
> repositoryId - The ID of a connected repo where the image to check resides
> imageId - The id of the image you wish to check.
> 
> All operations return once the operations has been committed to disk NOT when 
> the operation actually completes.
> This is done so that:
> - operation come to a stable state as quickly as possible.
> - In case where there is an SDM, only small portion of the operation actually 
> needs to be performed on the SDM host.
> - No matter how many times the operation fails and on how many hosts, you can 
> always resume the operation and choose when to do it.
> - You can stop an operation at any time and remove the resulting object 
> making a distinction between "stop because the host is overloaded" to "I 
> don't want that image"
> 
> This means that after calling any operation that creates a new image the user 
> must then call getImageStatus() to check what is the status of the image.
> The status of the image can be either optimized, degraded, or broken.
> "Optimized" means that the image is available and you can run VMs of it.
> "Degraded" means that the image is available and will run VMs but it might be 
> a better way VDSM can represent the underlying data. 
> "Broken" means that the image can't be used at the moment, probably because 
> not all the data has been set up on the volume.

So while an operation is executing asynchronously the state is broken?
How do you distinguish between an operation that ends in error and one
that is currently running?

> 
> Apart from that VDSM will also return the last persisted status information 
> which will conatin
> hostID - the last host to try and optimize of fix the image
> stage - X/Y (eg. 1/10) the last persisted stage of the fix.
> percent_complete - -1 or 0-100, the last persisted completion percentage of 
> the aforementioned stage. -1 means that no progress is available for that 
> operation.
> last_error - This will only be filled if the operation failed because of 
> something other then IO or a VDSM crash for obvious reasons.
>              It will usually be set if the task was manually stopped
> 
> The user can either be satisfied with that information or as the host 
> specified in host ID if it is still working on that image by checking it's 
> running tasks.
> 
> checkStorageRepository(self, repositoryId, options={}):
> A method to go over a storage repository and scan for any existing problems. 
> This includes degraded\broken images and deleted images that have no yet been 
> physically deleted\merged.
> It returns a list of Fix objects.
> Fix objects come in 4 types:
> clean - cleans data, run them to get more space.
> optimize - run them to optimize a degraded image
> merge - Merges two images together. Doing this sometimes
>         makes more images ready optimizing or cleaning.
>         The reason it is different from optimize is that
>         unmerged images are considered optimized.
> mend - mends a broken image
> 
> The user can read these types and prioritize fixes. Fixes also contain opaque 
> FIX data and they should be sent as received to
> fixStorageRepository(self, repositoryId, fix, options={}):
> 
> That will start a fix operation.

Just to clarify, you scan a repository that has 3 images on it.  You
will get a list of 3 fix objects, one for each image or a list of what
fixes should be run across the entire repository?

> 
> 
> All major operations automatically start the appropriate "Fix" to bring the 
> created object to an optimize\degraded state (the one that is quicker) unless 
> one of the options is
> AutoFix=False. This is only useful for repos that might not be able to create 
> volumes on all hosts (SDM) but would like to have the actual IO distributed 
> in the cluster.
> 
> Other common options is the strategy option:
> It has currently 2 possible values
> space and performance - In case VDSM has 2 ways of completing the same 
> operation it will tell it to value one over the other. For example, whether 
> to copy all the data or just create a qcow based of a snapshot.
> The default is space.
> 
> You might have also noticed that it is never explicitly specified where to 
> look for existing images. This is done purposefully, VDSM will always look in 
> all connected repositories for existing objects.
> For very large setups this might be problematic. To mitigate the problem you 
> have these options:
> participatingRepositories=[repoId, ...] which tell VDSM to narrow the search 
> to just these repositories
> and
> imageHints={imgId: repoId} which will force VDSM to look for those image ID 
> just in those repositories and fail if it doesn't find them there.

I'm guessing that you will be adding methods to query the existing
images, snapshots etc. ?

Thanks,
Tony
_______________________________________________
vdsm-devel mailing list
vdsm-devel@lists.fedorahosted.org
https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel

Reply via email to