Detailed query of CBT status

Is there any way, perhaps using a new tool that could be developed, to query the precise status of the CBT, such that it returns the total number/size of blocks it thinks have changed since the last full backup (i.e. the total size/number of blocks that now need to be backed up)?

The reason I ask is that the current incremental backup I’m running is predicting a ~7 hours run time, which seems a bit excessive for only ~40GB of changed blocks (by my reckoning).

For comparison I just ran an incremental ntfsclone|borg backup, which backup up ~550GB in ~4 hours, deduplicated down to ~20GB (from the first full backup), and that’s without any CBT. This type of backup does not mount the filesystem at all, and does not change any of its blocks, so I assume this did not affect the results of the subsequent UrBackup operation.

It might also be useful if the client could issue some kind of warning if something happens that causes the CBT to lose track of changed blocks (i.e. reset back to “all blocks”), or when it thinks there is suddenly a large change to the number of changed blocks, due to some problem with Windows.

As far as I know, nothing has happened on this system to cause the CBT to reset its list of changed blocks. There was a Windows update (monthly rollup kb3197868), but no crashes or other errors.

Well eventually the backup took 222 minutes for a 4.94GB incremental, which is basically what I would expect if CBT were disabled.

It probably did not show this log line, correct?

That is what it shows in that log line. If it does not show anything, it meant that CBT had to be reset. More serious issues are shown in the CBT status window. If it doesn’t show anything there it probably failed to write the bitmap during shutdown (e.g. normally because it had a power loss or bluescreen). Logging anything at this point is kind of problematic ;). If you have an SSD, turning on crash consistency may be an option.

Yes, that line is indeed missing from the log.

However, the backup I just launched says:

11/12/16 23:41  INFO  Starting incremental image backup..
11/12/16 23:41  DEBUG  Backing up SYSVOL..
11/12/16 23:41  DEBUG  Backing up SYSVOL done.
11/12/16 23:41  DEBUG  Backing up EFI System Partition...
11/12/16 23:41  DEBUG  Backing up EFI System Partition done.
11/12/16 23:41  INFO  Basing image backup on last incremental or full image backup
11/12/16 23:43  INFO  Change block tracking active. Max 11.0063 GB have changed.

So I guess something happened last time to reset the CBT.