Can I open an image and then redirect it to one of its snapshots?
I see that there is a snap_set method.
Do I understand correctly that I need to:
open the image
invoke snap_set method
invoke refresh method
Thanks in advance.
V.
On Wed, Jan 4, 2017 at 10:39 AM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
> I understood. Thanks!
>
> On Wed, Jan 4, 2017 at 10:34 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>> The loop isn't that big of a deal -- but you could eliminate it
>> entirely if you just index the in-memory snapshot table via the
>> SnapshotNamespace variant instead of just indexing snapshots by name
>> (e.g. ImageCtx::snap_ids key switches from a string to a namespace).
>> This would be required anyway since you might otherwise have duplicate
>> names between namespaces.
>>
>> On Wed, Jan 4, 2017 at 1:29 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>> It looks like next CDM is only next month. Let's try to figure it out in email.
>>>
>>>> Since you know which images are linked to the group and you know which
>>>> snapshots are in the group and which group snapshots are in the image,
>>>> you can reconcile any issues using the details in the
>>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>>> actual snapshot name (it could technically just be a randomly assigned
>>>> UUID).
>>>
>>> Let's say I have a consistency group and a snapshot of this group: CG
>>> and CGSNAP.
>>> Images in this snapshot I'll define as:
>>> CG.images[0] - image1
>>> CG.images[1] - image2
>>> CG.images[2] - image3
>>>
>>> Image snapshots in cg snapshot will be:
>>> CG.CGSNAP.snaps[0] - reference to snapshot of image 1
>>> CG.CGSNAP.snaps[1] - reference to snapshot of image 2
>>>
>>> Imagine that this snapshot was created, but wasn't finalized.
>>> CG.CGSNAP.state == PENDING.
>>> CG.CGSNAP.snaps.length == 0;
>>> I'll be writing in pseudo code.
>>>
>>> Now, let's say we want to remove this pending CGSNAP. This is the code
>>> how it's currently implemented:
>>>
>>> for (image: CG.images) {
>>> snap_name = image.id + "_" + CG.CGSNAP.id + "_" + CG.id // This name
>>> is unique because of uniqueness of the tuple (image.id, CG.CGSNAP.id,
>>> CG.id)
>>> remove_image_snapshot(snap_name);
>>> }
>>> remove_cg_snap(CGSNAP);
>>>
>>> However, if we don't rely on the name then this is how I envision the code:
>>>
>>> for (image: CG.images) {
>>> for (snap: image.snaps) {
>>> if (snap.namespace.cg_id == CG.id && snap.namespace.cg_snap_id ==
>>> CG.CGSNAP.id) { // this is our snapshot
>>> remove_image_snapshot(snap.name);
>>> }
>>> }
>>> }
>>> remove_cg_snap(CGSNAP);
>>>
>>> In this solution I don't like the internal loop.
>>> What do you think?
>>>
>>> Thanks,
>>> Victor.
>>>
>>>
>>> On Tue, Jan 3, 2017 at 6:56 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>> After starting the process of creating a group snapshot, you will
>>>> already have all the necessary data for the group snapshot namespace
>>>> [1] (group pool, group id, and group snapshot id) and the group
>>>> snapshot should be persistently recorded to disk as
>>>> GROUP_SNAPSHOT_STATE_PENDING.
>>>>
>>>> Looking at the snapshot create state machine [2], I don't see any
>>>> place that a crash (or similar failure) would matter before the actual
>>>> image snapshot record is created atomically. You would pass the fully
>>>> populated GroupSnapshotNamespace to snap_create, and if the snapshot
>>>> is created, it's linked to the group via that namespace and any
>>>> failures afterwards don't matter since they are linked -- if the
>>>> snapshot fails to be created, it isn't linked to the group but the
>>>> snapshot doesn't exist either so there isn't anything to clean up.
>>>>
>>>> Since you know which images are linked to the group and you know which
>>>> snapshots are in the group and which group snapshots are in the image,
>>>> you can reconcile any issues using the details in the
>>>> GroupSnapshotNamespace -- there shouldn't be any need to depend on the
>>>> actual snapshot name (it could technically just be a randomly assigned
>>>> UUID).
>>>>
>>>> Perhaps we could talk about this at a future RBD standup meeting that
>>>> you are able to join (or the next CDM).
>>>>
>>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L249
>>>> [2] https://github.com/ceph/ceph/blob/master/src/librbd/operation/SnapshotCreateRequest.h#L28
>>>>
>>>> On Tue, Jan 3, 2017 at 7:40 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>> Let's say we start creating a group snapshot.
>>>>> We invoke async snap_create method in Operations class.
>>>>> When we invoke this method we provide it with the snapshot name.
>>>>>
>>>>> While we are wating for the response we can be aborted.
>>>>> As a result we will be able to find the exact image snapshot using only its name
>>>>> as this was the only information we had at the time of running
>>>>> snap_create method.
>>>>>
>>>>> If snap_create was successful we will be able to find the snapshot
>>>>> otherwise we will not.
>>>>> However if we allow renaming snapshots from GroupSnapshotNamespace
>>>>> then we may not find the snapshot even if it
>>>>> was created successfully.
>>>>>
>>>>> On Fri, Dec 16, 2016 at 6:53 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>> Can you give a little background on this specific inconsistent case
>>>>>> you are referring to?
>>>>>>
>>>>>> On Thu, Dec 15, 2016 at 7:05 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>> Yes, but if image's snapshot is renamed then I'm not able to find this
>>>>>>> snapshot having only group's snapshot in an inconsistent state for
>>>>>>> example.
>>>>>>>
>>>>>>> V.
>>>>>>>
>>>>>>> On Thu, Dec 15, 2016 at 7:10 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>> I think I might be confused. When creating a group snapshot, we have
>>>>>>>> the ConsistencyGroupSnapshot that allows you to store the necessary
>>>>>>>> linkage between the image's snapshot and its associated group snapshot
>>>>>>>> [1]. Why not just name the image's snapshots to the same name as the
>>>>>>>> parent group snapshot name and search the snapshot's metadata to get
>>>>>>>> the linkage?
>>>>>>>>
>>>>>>>> [1] https://github.com/ceph/ceph/blob/master/src/cls/rbd/cls_rbd_types.h#L255
>>>>>>>>
>>>>>>>> On Tue, Dec 13, 2016 at 8:03 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>> Jason,
>>>>>>>>>
>>>>>>>>> My current implementation of consistency group snapshot feature names
>>>>>>>>> image snapshots like: <group_pool>_<group_id>_<group_snap_id>
>>>>>>>>> I rely on this fact when I need to remove a consistency group. It's
>>>>>>>>> necessary because if some of image snapshots were created, but the
>>>>>>>>> whole group snapshot operation failed,
>>>>>>>>> then the only way to find those dangling image snapshots is by this name.
>>>>>>>>>
>>>>>>>>> It means that we should forbid renaming snapshots from
>>>>>>>>> ConsistencyGroupSnapshot namespace.
>>>>>>>>>
>>>>>>>>> Another option is to allocate image snapshot ids during the creation
>>>>>>>>> of group snapshot, but this requires a major rewrite of the whole
>>>>>>>>> process of snapshot creation for images.
>>>>>>>>>
>>>>>>>>> What is your opinion on this?
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> V.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Nov 1, 2016 at 8:01 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>> I chatted with Xing on IRC this morning re: Cinder generic groups. It
>>>>>>>>>> sounds like RBD will need to support preserving the image's
>>>>>>>>>> consistency group snapshots even if the image is removed from the
>>>>>>>>>> group. In the OpenStack case, you won't have to worry about the image
>>>>>>>>>> being deleted while it still has associated group snapshots.
>>>>>>>>>>
>>>>>>>>>> We will also want to support being able to clone child images from a
>>>>>>>>>> group snapshot to ensure that we can thin provision new groups volumes
>>>>>>>>>> when creating a new group from a group snapshot. This means that the
>>>>>>>>>> group snapshots should be able to be protected/unprotected just like
>>>>>>>>>> standard user snapshots.
>>>>>>>>>>
>>>>>>>>>> On Mon, Oct 31, 2016 at 9:07 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>> Looking at the Cinder codebase, I don't see any such restriction that
>>>>>>>>>>> would prevent you from removing a volume from a consistency group that
>>>>>>>>>>> has associated snapshots. I would double-check on the OpenStack
>>>>>>>>>>> development mailing list if this is correct and is the intent. Worst
>>>>>>>>>>> case, the RBD driver could raise an exception if there are still
>>>>>>>>>>> consistency group snapshots associated to the image.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Fri, Oct 28, 2016 at 6:41 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>> Another thing that bothers me. When we remove an image from a consistency group.
>>>>>>>>>>>> Should we remove all snapshots of this image that were created as part
>>>>>>>>>>>> of a consistency group snapshot?
>>>>>>>>>>>>
>>>>>>>>>>>> The easiest solution would be to remove all snapshots that are in
>>>>>>>>>>>> GroupSnapshotNamespace and reference this consistency group.
>>>>>>>>>>>> I looked into cinder docs for this feature:
>>>>>>>>>>>> http://docs.openstack.org/admin-guide/blockstorage-consistency-groups.html
>>>>>>>>>>>>
>>>>>>>>>>>> But it's not clear to me which behavior cinder expects.
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks,
>>>>>>>>>>>> V.
>>>>>>>>>>>>
>>>>>>>>>>>> On Wed, Oct 26, 2016 at 6:16 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>> In a perfect world, it would be nice to add a new optional to "rbd
>>>>>>>>>>>>> snap ls" to show all snapshots (with a new column to indicate the
>>>>>>>>>>>>> associated namespace).
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Oct 25, 2016 at 11:07 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>> Question. When we print out snapshots of an image, should the group
>>>>>>>>>>>>>> snapshots be listed, or should they be marked as special snapshots?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>> V.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 3:14 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>> Ok. I didn't have any intention to throw exceptions.
>>>>>>>>>>>>>>> I was more concerned about whether it's ok to allocate and delete
>>>>>>>>>>>>>>> objects or I should use smart pointers.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Mon, Oct 10, 2016 at 7:18 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>> The only place exceptions are routinely used is within the "::decode"
>>>>>>>>>>>>>>>> functions. I would prefer to see the code not throwing new exceptions
>>>>>>>>>>>>>>>> on purpose.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Fri, Oct 7, 2016 at 2:26 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>> Are any exceptions used in librbd code? Should the code be exception safe?
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>>>>> V.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> On Fri, Sep 16, 2016 at 10:37 AM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>> On Thu, Sep 15, 2016 at 7:17 PM, Victor Denisov <vdenisov@xxxxxxxxxxxx> wrote:
>>>>>>>>>>>>>>>>>>> if (struct_v >= 5) {
>>>>>>>>>>>>>>>>>>> ::decode(snapshot_namespace, p);
>>>>>>>>>>>>>>>>>>> } else {
>>>>>>>>>>>>>>>>>>> snapshot_namespace = cls::rbd::UserSnapshotNamespace();
>>>>>>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> then code for ::encode function of cls_rbd_snap would change accordingly:
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> instead of
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> boost::apply_visitor(cls::rbd::EncodeSnapshotTypeVisitor(bl),
>>>>>>>>>>>>>>>>>>> snapshot_namespace);
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> I would do:
>>>>>>>>>>>>>>>>>>> ::encode(snapshot_namespace, bl);
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> +1 -- looks good to me
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>> Jason
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>> Jason
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Jason
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Jason
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Jason
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Jason
>>>>
>>>>
>>>>
>>>> --
>>>> Jason
>>
>>
>>
>> --
>> Jason
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