CBT Questions


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RayG
RayG
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Now that CBT will persist across reboots etc. I have noticed the following side effect from the way I had things set up for my backups.

I have a scheduled task that does an INC Forever every day. If that task is left to run on its own it will quite happily use CBT.

When I make a configuration change or Windows gets an update (Microsoft or otherwise) I run a different task to put that backup in a different folder and that one has a GFS base.

I notice that when I do this CBT is then no longer used by the next INC Forever, and will never be use by the second GFS backup.

CBT appears to be based on a sequence number and if things don't match then no CBT is possible

Is there a was Macrium can retain information so that multiple methods of a backup for the same source can make use of CBT.

A secondary question to this is how long can it be between backups before the CBT trail can grow no larger. This may have a bearing on what is possible.

Regards
RayG
Windows10 Pro X64 V1809 B17763.134 MR v7.2.3858

jphughan
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In for the answers on this.  At least on 7.1, one of my clients who uses Incrementals Forever is able to use CBT with his backups that involve a daily disk rotation.  As long as the most recent backup on the destination had been created during that same Windows session, then CBT gets used, even though due to the daily disk rotation strategy the most recent backup on a given destination was never the last backup that Reflect had created; it is instead a backup that Reflect generated a week ago.  But maybe things are different on 7.2, intentionally or otherwise.

Edited 6 November 2018 3:02 PM by jphughan
JamieW
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RayG - 6 November 2018 2:38 PM
Now that CBT will persist across reboots etc. I have noticed the following side effect from the way I had things set up for my backups.

I have a scheduled task that does an INC Forever every day. If that task is left to run on its own it will quite happily use CBT.

When I make a configuration change or Windows gets an update (Microsoft or otherwise) I run a different task to put that backup in a different folder and that one has a GFS base.

I notice that when I do this CBT is then no longer used by the next INC Forever, and will never be use by the second GFS backup.

CBT appears to be based on a sequence number and if things don't match then no CBT is possible

Is there a was Macrium can retain information so that multiple methods of a backup for the same source can make use of CBT.

A secondary question to this is how long can it be between backups before the CBT trail can grow no larger. This may have a bearing on what is possible.

jphughan - 6 November 2018 2:56 PM
In for the answers on this.  At least on 7.1, one of my clients who uses Incrementals Forever is able to use CBT with his backups that involve a daily disk rotation.  As long as the most recent backup on the destination had been created during that same Windows session, then CBT gets used, even though due to the daily disk rotation strategy the most recent backup on a given destination was never the last backup that Reflect had created; it was instead a backup that Reflect had generated a week ago.  But maybe things are different on 7.2, intentionally or otherwise.

You are correct that CBT is based on a sequence number and Reflect uses this to determine if a CBT based backup is possible. If the sequence number stored in the most recent image in the set, matches the sequence number held by the CBT driver, then a CBT based backup is possible.

There are various events that cause the drivers sequence number to be modified. These include the volume being mounted and/or modified outside of CBT’s control (booting into Windows PE/RE, disabling CBT) or anything else that causes NTFS to modify its own internal checkpoint (failed transactions, dirty-shutdowns, etc).

With regard to the amount of time between backups, there isn’t any limitation imposed by CBT, so this isn’t really a concern when considering what is possible.

RayG
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JamieW - 6 November 2018 3:43 PM
There are various events that cause the drivers sequence number to be modified. These include the volume being mounted and/or modified outside of CBT’s control (booting into Windows PE/RE, disabling CBT) or anything else that causes NTFS to modify its own internal checkpoint (failed transactions, dirty-shutdowns, etc).

Thanks for the reply.

So if there is no limitation to CBT in terms of time or the number of changed blocks, CBT must update the sequence number when a backup takes place and that refers, I would suspect, to a pointer (of some sort) that defines where the next record for a block that changes after a particular backup starts. That said, the sequence number for another backup for the same drive/partition is still potentially valid if CBT knows that it has not been mounted/changed outside of CBT's knowledge it is just a different start point in CBT's record of changes. Would that be correct or am I simplifying to much? If that is the case would it not be possible for both backups to make use of CBT?



Regards
RayG
Windows10 Pro X64 V1809 B17763.134 MR v7.2.3858

Nick
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RayG - 6 November 2018 4:12 PM
JamieW - 6 November 2018 3:43 PM
There are various events that cause the drivers sequence number to be modified. These include the volume being mounted and/or modified outside of CBT’s control (booting into Windows PE/RE, disabling CBT) or anything else that causes NTFS to modify its own internal checkpoint (failed transactions, dirty-shutdowns, etc).

Thanks for the reply.

So if there is no limitation to CBT in terms of time or the number of changed blocks, CBT must update the sequence number when a backup takes place and that refers, I would suspect, to a pointer (of some sort) that defines where the next record for a block that changes after a particular backup starts. That said, the sequence number for another backup for the same drive/partition is still potentially valid if CBT knows that it has not been mounted/changed outside of CBT's knowledge it is just a different start point in CBT's record of changes. Would that be correct or am I simplifying to much? If that is the case would it not be possible for both backups to make use of CBT?


So if there is no limitation to CBT in terms of time or the number of changed blocks, CBT must update the sequence number when a backup takes place and that refers,...


There is no limitation on the number of changed blocks or time. There is no update to the CBT sequence when a backup is made. The only time the CBT  sequence is updated is if the file system is mounted on an OS without the CBT driver (such as WinPE/RE), a dirty shutdown,  or if the driver is stopped and restarted. Basically, it's only updated when continuous tracking cannot be guaranteed. 

It's entirely possible for multiple backups to make use of CBT. 

Kind Regards

Nick - Macrium Support

Edited 6 November 2018 4:25 PM by Nick
RayG
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Nick - 6 November 2018 4:20 PM
RayG - 6 November 2018 4:12 PM
JamieW - 6 November 2018 3:43 PM
There are various events that cause the drivers sequence number to be modified. These include the volume being mounted and/or modified outside of CBT’s control (booting into Windows PE/RE, disabling CBT) or anything else that causes NTFS to modify its own internal checkpoint (failed transactions, dirty-shutdowns, etc).

Thanks for the reply.

So if there is no limitation to CBT in terms of time or the number of changed blocks, CBT must update the sequence number when a backup takes place and that refers, I would suspect, to a pointer (of some sort) that defines where the next record for a block that changes after a particular backup starts. That said, the sequence number for another backup for the same drive/partition is still potentially valid if CBT knows that it has not been mounted/changed outside of CBT's knowledge it is just a different start point in CBT's record of changes. Would that be correct or am I simplifying to much? If that is the case would it not be possible for both backups to make use of CBT?


So if there is no limitation to CBT in terms of time or the number of changed blocks, CBT must update the sequence number when a backup takes place and that refers,...


There is no limitation on the number of changed blocks or time. There is no update to the CBT sequence when a backup is made. The only time the CBT  sequence is updated is if the file system is mounted on an OS without the CBT driver (such as WinPE/RE), a dirty shutdown,  or if the driver is stopped and restarted. Basically, it's only updated when continuous tracking cannot be guaranteed. 

It's entirely possible for multiple backups to make use of CBT. 

Hi Nick, Thanks for that clarification - I will make a note of what happens with the next backups.

Regards
RayG
Windows10 Pro X64 V1809 B17763.134 MR v7.2.3858

RayG
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@Nick, The original reason for my question must have been that I had booted into the recovery environment at some point and that is why CBT was not be used on the backup that caused me to start this thread. All is working as expected.


That said, is there a reason why CBT is not or cannot be used on differentials now that things appear to be working 100% across restarts/shutdowns and protected when a file system is mounted outside of CBT's view.

Regards
RayG
Windows10 Pro X64 V1809 B17763.134 MR v7.2.3858

jphughan
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RayG - 7 November 2018 3:27 PM
@Nick, The original reason for my question must have been that I had booted into the recovery environment at some point and that is why CBT was not be used on the backup that caused me to start this thread. All is working as expected.


That said, is there a reason why CBT is not or cannot be used on differentials now that things appear to be working 100% across restarts/shutdowns and protected when a file system is mounted outside of CBT's view.

CBT is used on Differentials, as long as the parent Full was captured more recently than the CBT driver's monitoring history was purged.

RayG
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jphughan - 7 November 2018 3:29 PM

CBT is used on Differentials, as long as the parent Full was captured more recently than the CBT driver's monitoring history was purged.

Ah! I had not thought of that one. OK more watching/monitoring will ensue.


Regards
RayG
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