<![CDATA[Problem with differential restore]]>When I try to perform a differential restore I get this error:
VDI_INCOMPATIBLE_TYPE(OpaqueRef:94df0a4b-69ba-4ef5-adb3-21c5259ea0b1, CBT metadata)
Regular restore appears to be working.
Any advice please?

]]>https://xcp-ng.org/forum/topic/9728/problem-with-differential-restoreRSS for NodeFri, 12 Jun 2026 20:21:05 GMTThu, 03 Oct 2024 13:54:24 GMT60<![CDATA[Reply to Problem with differential restore on Fri, 18 Oct 2024 16:05:21 GMT]]>@frank-s Think of it like this...

You take the original backup with snapshot on October 1st.

You then have a differential backup on October 8th. That differential only writes the changes that make the state of the server on October 8th different (hence the term differential) from the state of the server as it was on the full snapshot on October 1st.

Now you delete the snapshot of the full system state taken on October 1st, leaving only the October 8th differential.

It's now October 15th and you want to restore something from the October 8th differential and you figure you'll just make a new full snapshot from October 15th and then try to apply the October 8th differential. However, this won't work because the differential from October 8th will be missing key reference points it will be looking for in order to overlay its changes onto the snapshot. What else on that server changed from October 1st to October 15th that isn't contained in the differential? What changes occurred from October 8th to October 15th that are newer than what is on the differential? You could, potentially, brick your entire system if the differential started overwriting changes it sees from its system state that are actually newer than the data it contains.

Differentials are entirely dependent on the full snapshot on which they are based. Any new snapshot taken after their creation will be totally foreign to the differential... those differentials will be looking for very specific system states that existed at the time the original snapshot was created, and those will be completely different from the system state as it will appear on a new snapshot created after the differential.

]]>https://xcp-ng.org/forum/post/84470https://xcp-ng.org/forum/post/84470Fri, 18 Oct 2024 16:05:21 GMT<![CDATA[Reply to Problem with differential restore on Thu, 17 Oct 2024 18:00:54 GMT]]>@olivierlambert said in Problem with differential restore:

No, because it's a planned feature. In short, XOA will act as an temporary SR so you can instantly start the backup VM, then migrate it to the target storage.

That’s great get InstantRestore!!!!

]]>https://xcp-ng.org/forum/post/84415https://xcp-ng.org/forum/post/84415Thu, 17 Oct 2024 18:00:54 GMT<![CDATA[Reply to Problem with differential restore on Thu, 17 Oct 2024 09:26:19 GMT]]>You will create a snapshot on the current state of the VM. Which has changed since the last snapshot. So this new snapshot has nothing to do with the previous/removed one, block changed. If you apply a diff from the old/removed snap on top of the new snapshot, what do you think will be the result?

]]>https://xcp-ng.org/forum/post/84390https://xcp-ng.org/forum/post/84390Thu, 17 Oct 2024 09:26:19 GMT<![CDATA[Reply to Problem with differential restore on Thu, 17 Oct 2024 09:07:31 GMT]]>@olivierlambert <The snapshot is deleted. You need a reference point to do differential>. So, since the snapshot is deleted, create a new one (snapshot) as part of the restore process and use that for the reference - then delete it when done.

]]>https://xcp-ng.org/forum/post/84389https://xcp-ng.org/forum/post/84389Thu, 17 Oct 2024 09:07:31 GMT<![CDATA[Reply to Problem with differential restore on Thu, 17 Oct 2024 06:47:49 GMT]]>Create a snapshot against which reference? The snapshot is deleted. You need a reference point to do differential. That reference is deleted when you remove the snapshot data.

Differential means differential against something, a reference. If you don't have a reference, it doesn't make sense. It's like guess a number after "minus 2" operation. What is that number? If you don't have the original number, it's impossible to apply "minus 2" on it.

]]>https://xcp-ng.org/forum/post/84383https://xcp-ng.org/forum/post/84383Thu, 17 Oct 2024 06:47:49 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 22:21:43 GMT]]>@olivierlambert Agreed, but in the case where the snapshot has been deleted, why can't the differential restore process simply create a snapshot from the vm and use that instead?

]]>https://xcp-ng.org/forum/post/84378https://xcp-ng.org/forum/post/84378Wed, 16 Oct 2024 22:21:43 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 18:38:04 GMT]]>That's true as long as you keep the snapshot data, which is not the case in NBD+purge data.

]]>https://xcp-ng.org/forum/post/84353https://xcp-ng.org/forum/post/84353Wed, 16 Oct 2024 18:38:04 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 16:52:35 GMT]]>@olivierlambert So, earlier in this thread, florent said "differential restore work by not transferring the data that the snapshot and the backup have in common, without reading any of those
it clone the last snapshot, an then revert the block changed between the older backup and the snapshot". If this is true (and I'm sure it is) why can't the differential restore system create the missing snapshot and use that to complete the differential restore?

]]>https://xcp-ng.org/forum/post/84347https://xcp-ng.org/forum/post/84347Wed, 16 Oct 2024 16:52:35 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 15:55:44 GMT]]>I'm not sure to follow. You need a point of reference in time to restore. If you start from a new snapshot, and apply the diff blocks (from XO backup) on top of it, it will be complete nonsense.

]]>https://xcp-ng.org/forum/post/84342https://xcp-ng.org/forum/post/84342Wed, 16 Oct 2024 15:55:44 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 15:51:28 GMT]]>@olivierlambert No, not recreating the snapshot from the CBT metadata but simply creating a new temporary snapshot, perform differential restore and delete the temporary snapshot when done.

]]>https://xcp-ng.org/forum/post/84341https://xcp-ng.org/forum/post/84341Wed, 16 Oct 2024 15:51:28 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 14:58:39 GMT]]>Recreating the snapshot from the CBT metadata? The problem is the CBT metadata doesn't make sense alone, only compared to the data saved by XO. So this will need to read a lot of data between XO and the host, not sure it will be faster at all (probably the opposite)

]]>https://xcp-ng.org/forum/post/84332https://xcp-ng.org/forum/post/84332Wed, 16 Oct 2024 14:58:39 GMT<![CDATA[Reply to Problem with differential restore on Wed, 16 Oct 2024 14:53:29 GMT]]>@frank-s So- I have been thinking about this. If an NBT/CBT backup is set to destroy the snapshot, would it be possible to make differential restore work by having the restore process create the snapshot it needs, perform the differential restore and then delete the snapshot?

]]>https://xcp-ng.org/forum/post/84331https://xcp-ng.org/forum/post/84331Wed, 16 Oct 2024 14:53:29 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 17:27:44 GMT]]>Thank you.

]]>https://xcp-ng.org/forum/post/83526https://xcp-ng.org/forum/post/83526Thu, 03 Oct 2024 17:27:44 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 17:26:36 GMT]]>No, because it's a planned feature. In short, XOA will act as an temporary SR so you can instantly start the backup VM, then migrate it to the target storage.

]]>https://xcp-ng.org/forum/post/83525https://xcp-ng.org/forum/post/83525Thu, 03 Oct 2024 17:26:36 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 17:24:09 GMT]]>Thank you. Is there somewhere I can read about this instant restore feature?

]]>https://xcp-ng.org/forum/post/83524https://xcp-ng.org/forum/post/83524Thu, 03 Oct 2024 17:24:09 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 17:21:21 GMT]]>You can't have CBT/flush snap + diff restore. In your case, our future instant restore feature might be one you seek.

]]>https://xcp-ng.org/forum/post/83519https://xcp-ng.org/forum/post/83519Thu, 03 Oct 2024 17:21:21 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 16:26:59 GMT]]>@frank-s Soz - I meant differential restores...

]]>https://xcp-ng.org/forum/post/83514https://xcp-ng.org/forum/post/83514Thu, 03 Oct 2024 16:26:59 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 15:56:52 GMT]]>@florent
I just did a delta backup on a small VM but chose NOT to delete the snapshot. It completed quickly and I then tried a differential restore and it worked. I also tried to do a differential restore on a delta backup made yesterday when the snapshot was deleted - this also worked. Will it be possible in the future to make differential backups work without keeping the snapshot? Is such a thing possible?
Thanks,
Frank.

]]>https://xcp-ng.org/forum/post/83510https://xcp-ng.org/forum/post/83510Thu, 03 Oct 2024 15:56:52 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 15:18:23 GMT]]>@frank-s said in Problem with differential restore:

So my guess is it will work if I choose not to delete the snapshot??? If that is correct it is a pity as differential restore is very fast compared to regular restore. Differential restore, for instance, would be a brilliant way to recover quickly from a ransomware attack. Also, deleting the snapshot makes coalescing much faster. Am I correct in my assumptions? Is there a way it could be made to work without the snapshot?
Thank you,
Frank.

differential restore work by not transferring the data that the snapshot and the backup have in common, without reading any of those
it clone the last snapshot, an then revert the block changed between the older backup and the snapshot.

In theory, if you run a delta backup without destroying the data, it should provide the anchor to have this work.

]]>https://xcp-ng.org/forum/post/83501https://xcp-ng.org/forum/post/83501Thu, 03 Oct 2024 15:18:23 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 15:10:42 GMT]]>I will backup again without deleting the snapshot and then attempt a differential restore.
I will update this thread when done.

]]>https://xcp-ng.org/forum/post/83498https://xcp-ng.org/forum/post/83498Thu, 03 Oct 2024 15:10:42 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 15:08:20 GMT]]>I have the impression it's one or another, to choose between pro and cons on the two.

]]>https://xcp-ng.org/forum/post/83496https://xcp-ng.org/forum/post/83496Thu, 03 Oct 2024 15:08:20 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 15:07:24 GMT]]>So my guess is it will work if I choose not to delete the snapshot??? If that is correct it is a pity as differential restore is very fast compared to regular restore. Differential restore, for instance, would be a brilliant way to recover quickly from a ransomware attack. Also, deleting the snapshot makes coalescing much faster. Am I correct in my assumptions? Is there a way it could be made to work without the snapshot?
Thank you,
Frank.

]]>https://xcp-ng.org/forum/post/83495https://xcp-ng.org/forum/post/83495Thu, 03 Oct 2024 15:07:24 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 14:57:15 GMT]]>Thanks, it's a lot more clear now 🙂 I don't think diff restore works with CBT as we remove the snapshot data. But it's a good question so we update the UI to reflect that and/or document it. @florent will confirm

]]>https://xcp-ng.org/forum/post/83493https://xcp-ng.org/forum/post/83493Thu, 03 Oct 2024 14:57:15 GMT<![CDATA[Reply to Problem with differential restore on Thu, 03 Oct 2024 14:53:51 GMT]]>@olivierlambert
I am using XO from the sources.
commit a9b99 Master, commit 30172
When I try to restore I select the appropriate backup (I have done this with both internal NFS remote and also with s3 remote). I select the SR that the backed up VM is on and turn on "use differential restore". When I click OK it fails immediately with the following error: <VDI_INCOMPATIBLE_TYPE(OpaqueRef:6ef1574a-ffc6-412b-bf6b-6804bacc0523, CBT metadata)>
This also happens on a completely different installation (different XCP different XO different client).
It's been a while since I used differential restore. It seems odd that when turned on I can select any destination SR. My understanding is that the restore needs the same SR as the original VM - that's what I selected.
When I last used differential restore I was not using NBD/CBT.
Regular restore seems to be working.

20ae3ebd-3801-485c-8b59-9193e06c2c56-image.png

Thanks,
Frank.

]]>https://xcp-ng.org/forum/post/83492https://xcp-ng.org/forum/post/83492Thu, 03 Oct 2024 14:53:51 GMT