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

----- Original Message ----- > From: "Deepak C Shetty" <deepakcs(a)linux.vnet.ibm.com&gt; > To: "Saggi Mizrahi" <smizrahi(a)redhat.com&gt; > Cc: "Shu Ming" <shuming(a)linux.vnet.ibm.com&gt;, "engine-devel" <engine-devel(a)ovirt.org&gt;, "VDSM Project Development" > <vdsm-devel(a)lists.fedorahosted.org&gt;, "Deepak C Shetty" <deepakcs(a)linux.vnet.ibm.com&gt; > 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(a)linux.vnet.ibm.com&gt; >>> To: "Saggi Mizrahi" <smizrahi(a)redhat.com&gt; >>> Cc: "VDSM Project Development" >>> <vdsm-devel(a)lists.fedorahosted.org&gt;, "engine-devel" >>> <engine-devel(a)ovirt.org&gt; >>> 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.