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[Tim <question668407@xxxxxxxxxxxxxxxxxxxxx>]

Question #668407 on Duplicity changed:
https://answers.launchpad.net/duplicity/+question/668407

Description changed to:
On a fresh Ubuntu 18.04 system I decided to give Deja-Dup a go. It's
just a GUI for Duplicity. About 850GB of data needed to be backed up.
Source SSD was NVMe. Destination SSD was SATA. Initial (full) backup
took about 7 hours.

The next day I did nothing more than check mail and install an
application — which added ~230MB — before running Deja-Dup again.

Deja-Dup ran for ~39 minutes loading a single core at 35–70% for the
entire duration.

Duplicity was invoked three times:

    The Scanning phase pegged a core at 100% for 18 minutes.
    The Backing Up phase pegged a core at 100% for 16 minutes.
    The Verifying phase pegged a core at 100% for 5 minutes.

This is on a new computer with plenty of RAM. The backup was not
encrypted.

Now, I expect initial (full) backups to take a while, and that's fine.
What I don't expect is for ~230MB of new data to take ~39 minutes to be
backed up (and consume over a collective core-hour of CPU time).

I ran a manual backup after negligible changes (a few KB of new mail)
and the time taken was the same (~39 minutes). Thus the time taken seems
to have little to do with the amount of new data that needs to be backed
up.

I ran iotop whilst that last backup was proceeding, and the Scanning
phase Read 7.36GB, the Backup phase Read 868MB and Wrote 5.55MB, and the
Verifying phase seemed to neither Read nor Write.

Is something wrong or broken? Should incremental backups of minor
changes take that much time to perform? I was expecting something under
5 minutes, not ~39. Why is it taking so long?

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