Restore is extremely slow


I just tried a restore and the speed is extremely slow (<3 mbps on LAN).

The setup is:
Installed on debian-based NAS (ReadyNAS)
Source: A folder containing a single 300 MB file and another 1KB file.
Destination: FTP share on another NAS

The backup speed is pretty speedy (~20MB/s). And I have checked that FTP speeds are also good between the two machines.

However, restore speed is SLOOW even when selecting to only restore the 1KB file.
There is no particular CPU, network or disk load on the machines in either end, so I don’t think it has to do with decryption.
I have tried various other protocols (SFTP, SSH, Webdav), but I recon that FTP has the lowest overhead.

Any ideas how to improve this?

Hello, what CPU does NAS have?
And it is possible that first backup was very slow too? And only the following backups are fast?

The CPU is an Atom D410 x64 @ 1.66 GHz

But as stated, the backup ran fast at around 20MB/s (during first run).
There was no mentionable load on the CPU even during the first backup, and also not during restore.

Were these files created, backed up, then never changed, or has there been a stream of changes to them?

The design is good at isolating changed parts of files, bundling only those, and uploading to the destination, however the result is that a restore may have to gather file pieces done at various times, along with updates originally taken from other files of the same backup then bundled in the same bundle (which is a dblock file).

Remote Volume Size discusses this effect, and gets into some of the tradeoffs of smaller and bigger dblocks.

I’m not sure how speed is calculated, but a proper calculation IMO would ignore downloads for the other files, meaning network download speed could be high, but data accumulation speed for a specific file could be low.

Of course it could also be something else. You can watch ReadyNAS Network (see System --> Performance).

Duplicati has a log for every job (I assume you use web UI and perhaps email). BackendStatistics might help understanding of what’s going on, however there may be little help. Restores can be network transfer heavy.

Getting back to the opening point, if the files were not updated over time, the speed issue may lie elsewhere. There’s also a local database that sometimes is disk-limited, but I think that hits primarily on backup creation.