Re: [Engine-devel] Domain rescan action question

From: "Ricky Hopper" <Ricky.Hopper(a)netapp.com&gt; To: "Dan Yasny" <dyasny(a)redhat.com&gt; Cc: engine-devel(a)ovirt.org, "Itamar Heim" <iheim(a)redhat.com&gt;, "Andrew Cathrow" <acathrow(a)redhat.com&gt; Sent: Wednesday, 1 August, 2012 8:36:09 PM Subject: Re: [Engine-devel] Domain rescan action question On 8/1/12 10:05 AM, "Dan Yasny" <dyasny(a)redhat.com&gt; wrote: > > >----- Original Message ----- >> From: "Ricky Hopper" <Ricky.Hopper(a)netapp.com&gt; >> To: "Dan Yasny" <dyasny(a)redhat.com&gt; >> Cc: engine-devel(a)ovirt.org, "Itamar Heim" <iheim(a)redhat.com&gt;, >> "Andrew >>Cathrow" <acathrow(a)redhat.com&gt; >> Sent: Wednesday, 1 August, 2012 4:56:45 PM >> Subject: Re: [Engine-devel] Domain rescan action question >> >> >> >> On 8/1/12 9:42 AM, "Dan Yasny" <dyasny(a)redhat.com&gt; wrote: >> >> > >> > >> >----- Original Message ----- >> >> From: "Ricky Hopper" <Ricky.Hopper(a)netapp.com&gt; >> >> To: "Dan Yasny" <dyasny(a)redhat.com&gt;, "Andrew Cathrow" >> &gt;&gt;&lt;acathrow(a)redhat.com&gt; >> >> Cc: engine-devel(a)ovirt.org, "Itamar Heim" <iheim(a)redhat.com&gt;, >> >> "Ricky >> >>Hopper" <Ricky.Hopper(a)netapp.com&gt; >> >> Sent: Wednesday, 1 August, 2012 4:34:53 PM >> >> Subject: Re: [Engine-devel] Domain rescan action question >> >> >> >> >> >> >> >> On 8/1/12 5:59 AM, "Dan Yasny" <dyasny(a)redhat.com&gt; wrote: >> >> >> >> > >> >> > >> >> >----- Original Message ----- >> >> >> From: "Andrew Cathrow" <acathrow(a)redhat.com&gt; >> >> >> To: "Itamar Heim" <iheim(a)redhat.com&gt;, "Dan Yasny" >> >> >> <dyasny(a)redhat.com&gt;, >> >> >>"Ricky Hopper" <Ricky.Hopper(a)netapp.com&gt; >> >> >> Cc: engine-devel(a)ovirt.org >> >> >> Sent: Wednesday, 1 August, 2012 12:24:42 AM >> >> >> Subject: Re: [Engine-devel] Domain rescan action question >> >> >> >> >> >> >> >> >> >> >> >> ----- Original Message ----- >> >> >> > From: "Itamar Heim" <iheim(a)redhat.com&gt; >> >> >> > To: "Ricky Hopper" <Ricky.Hopper(a)netapp.com&gt; >> >> >> > Cc: engine-devel(a)ovirt.org >> >> >> > Sent: Tuesday, July 31, 2012 4:44:34 PM >> >> >> > Subject: Re: [Engine-devel] Domain rescan action question >> >> >> > >> >> >> > On 07/31/2012 11:30 PM, Hopper, Ricky wrote: >> >> >> > > Hey all, >> >> >> > > >> >> >> > > As I'm making progress with the domain rescan >> >> >> > > functionality, >> >> >> > > I've >> >> >> > > realized that I'm unsure what to do with any disks that >> >> >> > > are >> >> >> > > detected on >> >> >> > > the domain. Should I add them back into the database to >> >> >> > > be >> >> >> > > listed >> >> >> > > as >> >> >> > > floating disks, or should I just return a list of disk >> >> >> > > images >> >> >> > > to >> >> >> > > be >> >> >> > > attached to whatever the caller of the query needs? >> >> >> > > >> >> >> > > - Ricky >> >> >> > >> >> >> > i'm not sure they should be added automatically. >> >> >> > I think a dialog[1] showing orphan disks/images on the >> >> >> > storage >> >> >> > domain >> >> >> > for user to choose which to import as 'floating' disks >> >> >> > would >> >> >> > be >> >> >> > better >> >> >> > than auto importing them. >> >> >> > >> >> >> > there is also the reverse of flagging existing disks as >> >> >> > 'missing' >> >> >> > in >> >> >> > storage? >> >> >> > >> >> >> >> >> >> Perhaps we should start a feature page to discuss and better >> >> >> scope >> >> >> it. >> >> >> There is a feature page that we could expand, it doesn't >> >> >> discuss >> >> >> the >> >> >> notion of importing those disks which is certainly something >> >> >> we >> >> >> need >> >> >> to address. >> >> >> >> >> >> >> >> >> http://wiki.ovirt.org/wiki/Features/Orphaned_Images >> >> > >> >> >The original idea was to scan the storage domains and compare >> >> >the >> >> >images >> >> >lists to the database, thus getting a list of images no longer >> >> >relevant >> >> >and scrubbing the storage. This will actually be addressed >> >> >properly >> >> >in >> >> >the future (Ayal can elaborate on that) but for now this is >> >> >needed >> >> >at >> >> >least for that use case. >> >> > >> >> > >> >> >As I understand, the conversation here is about trying to take >> >> >an >> >> >already >> >> >populated SD (from another setup I suppose), scanning it and >> >> >putting >> >> >it >> >> >into RHEV? >> >> >> >> As I understood it, the purpose of this functionality wasn't to >> >> find >> >> images which should be removed from storage, but to find images >> >> on >> >> the >> >> domain that oVirt was unaware of and importing them for use >> >> (for >> >> instance, >> >> if a disk was created outside of oVirt on the domain). If one >> >> of >> >> the >> >> use >> >> cases for this feature is also the orphaned images mentioned on >> >> the >> >> feature page, that may expand the functionality into a separate >> >> domain >> >> scrub and storage import, both of which would call the rescan >> >> (meaning the >> >> rescan would not actually add to the database, but instead >> >> return >> >> a >> >> list >> >> of "orphaned" disk images). >> >> >> >> Another solution would be to import all disk images into the >> >> database >> >> either way, and let the user delete any orphaned images from >> >> the >> >> GUI. >> > >> >I think are nice to have, but the problem with the scanning is >> >that >> >if >> >we're not scanning a master domain or an export domain, all we >> >will >> >see >> >is a bunch of images with no context or even hints as to where >> >they >> >belong. The data that makes it all usable is in the engine >> >database >> >and >> >in the ovf files on the master domain. >> > >> >This is why I stopped at the orphaned images part of the feature >> >- >> >because there it's feasible, I would rely on the engine database >> >for >> >image ID comparisons. >> > >> >If we present a user with a list of nameless disks, I doubt it >> >will >> >be of >> >any use. >> >> The way this would work is by comparing a list of disk images from >> vdsm >> and from oVirt's database, finding the ones vdsm returns that >> oVirt >> doesn't have, and then either adding or returning those images. So >> oVirt's >> db will be used in the comparison. > >This will work only when scanning storage domains already attached >and in >use by the current oVirt setup. What I am talking about is what will >happen if a LUN that used to be a SD in another oVirt setup is >discovered >and scanned, with no engine db to compare with. If we don't consider >such >a use case, life is definitely quite easy, and we're basically >within the >scope of the orphaned images feature This use case should definitely be considered, maybe have a separate case where the rescan would return all "compatible" disks (i.e. disks that aren't just partial snapshots and the like) if the domain has not yet been mounted. Essentially, it would run the same comparison, but compare against an empty list rather than a list of disks. There's no way it's as simple as that (I'm unsure of the methods oVirt uses to mount a domain), but it's a good starting point.

> >> >> As far as presenting the user with nameless disks, that's a point >> I >> hadn't >> considered; we could generate some sort of placeholder metadata >> upon >> addition to show the user that these are new/orphaned disks that >> were >> found on the storage domain. Is it safe to assume that the disks >> discovered by this feature won't be attached to anything? > >The oVirt paradigm says "if it isn't in the engine db, it's not >ours", so >any LV or image we discover that is missing from the DB or the >snapshot >chain of the image in the DB, is nameless, and orphaned. > >Such an image on a current SD, belonging to a working oVirt setup is >definitely an orphaned image. Attaching these to VMs is usually also >useless, because they are more often than not discarded snapshots >that >didn't get discarded cleanly for some reason. > > >Now, if we want to make this usable, we might want to actually check >the >qcow2 metadata of the image to see whether it's a mid-chain snapshot >(and >if so it's probably just a candidate for cleanup), or a standalone >qcow2 >or raw image, and then we can move on with the virt-* tools, to find >out >the image size and the filesystems it contains. This will at least >provide the user with some usable information about the detected >image. >If we're talking about scanning an SD that doesn't presently belong >to >the current oVirt setup, then this is even more relevant, because >all of >the images will have no VM-related context. We're currently working on having disks created outside of the oVirt environment, so not all orphaned disks on the existing storage domain will be artifacts of supposedly-deleted data.

For our use case, disk images created by us will be able to be imported into oVirt and attached to a VM created through the engine. Because of this, saying "if it isn't in the engine db, it's not ours" wouldn't necessarily be true. When you talk about checking the metadata, does either oVirt or vdsm have a simple way to do this? A query of some sort would be ideal for this, as it could be run for each image as a qualifier for import.

Also, as far as writing the functionality itself, I'm gathering that it should be structured as a query to return these orphaned images, which can then be acted upon/added to the database through a separate command after checking the validity of each image?

> >> > >> > >> >> > >> >> >> >> >> >> > >> >> >> > [1] or a subtab on the storage domain. >> >> >> > >> >> >> > _______________________________________________ >> >> >> > Engine-devel mailing list >> >> >> > Engine-devel(a)ovirt.org >> >> >> > http://lists.ovirt.org/mailman/listinfo/engine-devel >> >> >> > >> >> >> >> >> > >> >> >-- >> >> > >> >> > >> >> > >> >> >Regards, >> >> > >> >> >Dan Yasny >> >> >Red Hat Israel >> >> >+972 9769 2280 >> >> >> >> >> > >> >-- >> > >> > >> > >> >Regards, >> > >> >Dan Yasny >> >Red Hat Israel >> >+972 9769 2280 >> >> > >-- > > > >Regards, > >Dan Yasny >Red Hat Israel >+972 9769 2280