CBT & Boot Drive


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NineOfSeven
NineOfSeven
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This article seems to stress CBT as useful for large files where program(s) make raw access to modify blocks within the file.

https://blog.macrium.com/macrium-reflect-changed-block-tracker-ab2de9cb9d8c

What about boot drives?  Can/Should CBT be used on the Windows C: drive?  Does it matter if pagefile, swapfile, hiberfile are set up on that drive or not?  Can CBT be set on a per-drive basis, or is it either on or off system-wide?  How much does it degrade the performance of individual drives or the whole system?

jphughan
jphughan
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CBT delivers its largest benefit when you are creating frequent Diff/Inc backups, such as every hour or less, and/or when you are making image backups of volumes that contain working with large files. The reason is that if you do NOT use CBT, then Reflect has to use the “Looking for changes” method whenever you create a Diff/Inc backup. That involves analyzing the file system to figure out what files are new or changed. That part doesn’t take very long, but that doesn’t tell Reflect what exact portions of the changed files are actually different. That has to be determined by scanning the files as the backup proceeds. So if you make frequent backups, you incur that time overhead frequently, and if you’re backing up large files, then Reflect has to scan the entirety of large files even if the actual changes are minimal. By comparison, when you use CBT, Reflect already knows the exact blocks that have changed since the previous backup, so you can save time.

CBT can be used on NTFS partitions, including the C drive, and as of Reflect V8 it can also be used on ReFS partitions. It can also be disabled or enabled on a per-partition basis by opening Reflect, selecting the partition of interest, clicking the Actions item below it, and enabling or disabling CBT. Macrium posted a reply here providing some technical background to explain that the additional disk activity incurred by CBT is minimal. I haven’t seen anybody complain about CPU or memory utilization issues despite CBT having been around for a while. That said, I personally choose not to have it even installed on my systems because I simply don’t fall into the main use cases where it delivers a benefit, since I don’t make very frequent backups and don’t back up volumes with very large average file sizes. And since I subscribe to the concept of minimizing complexity to minimize potential problems, I don’t feel it’s a compelling value proposition for me. CBT is a low-level driver, and it has received its share of updates over time to address bugs and conflicts with other applications that created issues spanning a range of impact, and therefore not having it installed has saved me from being affected by at least some of those issues and has also saved me reboots on systems where downtime can be difficult to obtain. Since CBT is a driver, if a Reflect update contains a CBT update and you have it installed, then you’ll need to reboot your system. But if you don’t have CBT installed, then you won’t have to do that.

Edited 27 May 2021 4:10 AM by jphughan
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