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David Ramsey

Joined: 05-May-12 08:46
Messages: 48

I've been using QRecall for years, and my only complaint is the performance: on a boot volume with about 1.2TB of data, even incremental backups can take quite a while. From NVME->NVME, it can take upwards of 20 minutes, even if less than a gigabyte of data has changed since the last backup.

Carbon Copy Cloner, which I also use, has recently introduced a "Quick Update" feature that uses the operating system's transaction records, so that rather than doing a complete walk of the directoty tree, it can ask the OS which files have changed, and only back those up. A 20-minute backup with QRecall takes under 30 seconds with CCC.

(Yes, I realize they're doing different things.)

Still, it seems that implementing this feature has the potential to make backups much faster.
James Bucanek

Joined: 14-Feb-07 10:05
Messages: 1522

David Ramsey wrote:(Yes, I realize they're doing different things.)

You are correct, they are doing different things.

However, QRecall does use the filesystem history to quickly skip over folders that do not appear to have any changes, and it's done this since ... well ... filesystem history was introduced into OS X.

This is a bit of a complicated subject, so there are a few caveats.

First, QRecall does not blindly trust the filesystem history. There are known situations where the filesystem history can miss changes, and a "deep dive" into the file hierarchy is the only way to catch those changes.

On occasion, QRecall will ignore the filesystem history and perform an exhaustive search of the filesystem looking for changes. This can take a very long time. The default is to do this about once a week, so you'll occasionally see a capture take a lot longer than normal. In the log you'll see the message "Filesystem change history ignored" when it does this.

This interval can also be adjusted in the advanced settings. If you change the advanced setting "Filesystem Change History Trust Limit" to a shorter interval, it will perform this more often. If it's set to 0.0, then it will always ignore the change history and perform an exhaustive search on every capture.

You can also override this in a specific capture action. If you set the "Deep Scan" option, that specific capture will always ignore filesystem history.

In addition, you can set individual folders to ignore changes. Those changes can only be ignore for so long (typically 24 hours). This will cause QRecall to exhaustively search those specific folders. In the log you'll see the message "Deep scanning ignored folders" when that happens.

Finally, even when QRecall can skip over folders it knows haven't changed, it still has to compare the files now with those in the archive's history to determine the differences. Normally this is very quick, but if you have folders with thousands of items or a lot of layers (a 100 or more), then it will simply take some time to reconstruct the baseline picture of the folder before QRecall can start looking for what's changed.

I hope that helps explain some of the differences. Let us know if you have additional questions.

- QRecall Development -
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