[ovirt-devel] Re: [storage] how to find if a snapshot is in preview based on storage domain metadata only?

On Thu, Aug 27, 2020, 16:38 Tal Nisan <tnisan(a)redhat.com&gt; wrote: > > > On Fri, Aug 21, 2020 at 4:34 AM Germano Veit Michel <germano(a)redhat.com&gt; > wrote: > >> Hi, >> >> Is there a reliable way to figure out if a snapshot is in preview only >> using information obtained from the storage domain metadata? >> I'm trying to find a way to distinguish a problematic snapshot chain >> (double parent) from a snapshot in preview in order to improve dump-volume >> chains. >> >> Currently dump-volume-chains throws an error (DuplicateParentError) if a >> snapshot is in preview for the image, as there is a 'Y' shape split in the >> chain >> with 2 volumes (previous chain + preview) pointing to a common parent: >> >> image: dff0a0c0-b731-4e5b-9f32-d97310ca40de >> >> Error: more than one volume pointing to the same parent >> volume e.g: (_BLANK_UUID<-a), (a<-b), (a<-c) >> >> Unordered volumes and children: >> >> - e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38 <- >> 5eb2b29d-82d6-4337-8511-3c86705d566e >> status: OK, voltype: LEAF, format: COW, legality: LEGAL, >> type: SPARSE, capacity: 1073741824, truesize: 1073741824 >> >> - e0475853-4514-4464-99e7-b185cce9b67d <- >> deceff83-9d88-4f87-8304-d5bf74d119b1 >> status: OK, voltype: LEAF, format: COW, legality: LEGAL, >> type: SPARSE, capacity: 1073741824, truesize: 1073741824 >> >> - e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38 <- >> e0475853-4514-4464-99e7-b185cce9b67d >> status: OK, voltype: INTERNAL, format: COW, legality: >> LEGAL, type: SPARSE, capacity: 1073741824, truesize: 1073741824 >> >> - 00000000-0000-0000-0000-000000000000 <- >> e6c7bec0-53c6-4729-a4a0-a9b3ef2b8c38 >> status: OK, voltype: INTERNAL, format: RAW, legality: >> LEGAL, type: PREALLOCATED, capacity: 1073741824, truesize: 1073741824 >> >> From the engine side it's easy, but I'd need to solve this problem using >> only metadata from the storage. >> >> The only thing I could think of is that one of the volumes pointing to >> the common parent has voltype LEAF. Any better ideas? >> > don't think that there is any, Engine is the orchestrator and due to that > the info is only in the database > There is no good way, but you can look at the length of the chain, and the "ctime" value. For example if this was the original chain: a <- b <- c if we preview a: a <- b <- c a <- d You know that d is a preview volume. If we preview b, we will have two chains of same length: a <- b <- c a <- b <- d But the ctime value of d will be larger, since preview is created after the leaf was created. ctime is using time.time() so it is not affected by time zone changes but it may be wrong due to host time changes, so it is not reliable. Can you open a bug for this?