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#1 2021-06-04 14:18:58

kd.gundermann
Member
Registered: 2018-02-27
Posts: 20

Replica with large diff size

as we had a public holiday yesterday I expected that there would only small diffs in the VMs.
But I'm seeing some VMs with large diffs (almost full backup):

XSIBackup-DC 1.5.0.3
Action: replica=cbt
CBT enabled for all VMs

The Good:

UTC | Thu, 03 Jun 2021 23:00:29
1	[46] WinADS2	480.01 GB	2.81 MB	1	00:00:16	30720.55 MB/s	1	0
UTC | Wed, 02 Jun 2021 23:00:21
1	[46] WinADS2	480.01 GB	2.78 MB	1	00:00:11	44684.43 MB/s	1	0
UTC | Tue, 01 Jun 2021 23:00:26
1	[46] WinADS2	480.01 GB	2.76 MB	1	00:00:15	32768.58 MB/s	1	0

The Bad:

UTC | Fri, 04 Jun 2021 00:48:24
1	[77] Zoll-VM	60.01 GB	47.71 GB	1	00:18:16	56.06 MB/s	1	0
UTC | Thu, 03 Jun 2021 00:49:18
1	[77] Zoll-VM	60.01 GB	47.66 GB	1	00:19:10	53.43 MB/s	1	0
UTC | Wed, 02 Jun 2021 00:47:30
1	[77] Zoll-VM	60.01 GB	47.66 GB	1	00:17:23	58.91 MB/s	1	0

Zoll-VM is a Windows 10 VM with only 35% used disk space:

PS C:\Users\Zoll> Get-PSDrive

Name           Used (GB)     Free (GB) Provider      Root                                               
----           ---------     --------- --------      ----
C                  24,64         34,75 FileSystem    C:\

How can I diagnose why there is such a large diff ?

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#2 2021-06-04 22:40:24

admin
Administrator
Registered: 2017-04-21
Posts: 1,778

Re: Replica with large diff size

Maybe a full resync took place, can you share the full log?.

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#3 2021-06-07 09:35:45

kd.gundermann
Member
Registered: 2018-02-27
Posts: 20

Re: Replica with large diff size

You are right:

 /!\ Some changes were detected in the remote replicated VM a full sync will be performed now. 

I will try to --reset-cbt and report later

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#4 2021-06-07 15:40:21

admin
Administrator
Registered: 2017-04-21
Posts: 1,778

Re: Replica with large diff size

Well, that was very foreseable, now the question is, who or what?

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#5 2021-06-15 11:21:43

kd.gundermann
Member
Registered: 2018-02-27
Posts: 20

Re: Replica with large diff size

admin wrote:

Well, that was very foreseable, now the question is, who or what?

I think you are questioning who or what modified the remote replicated VM?
That's a good question, as the destination is on a Synology NAS Storage and is not mounted to any VMWare host.

I have tried to reset-cbt but seeing the problem again on these VMs:
- Qlik-VM
- Zoll-VM

I may send you the full xsibackup.log (I have found no way to attach a file to this post..)

PS: see also: https://33hops.com/forum/viewtopic.php?id=968

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#6 2021-06-15 14:08:19

admin
Administrator
Registered: 2017-04-21
Posts: 1,778

Re: Replica with large diff size

Yes, there's another post open with the same problem. As it's more recent let's stick to it to follow the issue.
When a CBT sync is performed, the .vmdk file descriptors need to be updated in the .map files of the replica to reflect the new CID.
When a subsequent sync cycle is run (c)XSIBackup-DC checks that the hash of the .vmdk file descriptors is the same as those stored in the corresponding .map files. When some discrepancy is detected, the CBT scheme is reinitilized.

There are mainly two reasons that could lead to this:

1/ The remote VM was switched on without a test snapshot (--options=R) and the CID changed as per the VM activity. This is the simplest explanation and the first we think of, although at this point it seems clear that is not the case.

2/ The remote hashes of the .vmdk descriptor files failed to be updated. This is the most likely cause as of today. That's why we need the full log. If this is the cause, then there must be some special condition: it could be some bug or some faulty component of the ESXi shell (which we have found to be relatively frequent). Having the exact ESXi version and the rest of details present in the log is fundamental to delve into the issue.

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#7 2021-06-15 14:59:37

kd.gundermann
Member
Registered: 2018-02-27
Posts: 20

Re: Replica with large diff size

so, how could I send you the log ?

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#8 2021-06-16 08:21:54

admin
Administrator
Registered: 2017-04-21
Posts: 1,778

Re: Replica with large diff size

You are a registered user, contact support, we'll publish an excerpt here

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