Speed issues during backup


I need to backup some 30 files with total size 800GB. Those files are located in a NAS device and backup destination is Azure. Backup speed is about 2MB/s which I believe is really slow.

Duplicati is running on a Windows Server 2012 machine with 32GB RAM and a 12 core Intel Xeon processor. Internet connection at the site is 600Mbps (75MB/s) and a test of uploading content to Azure was using most of this bandwith, so Internet connection speed does not seem to be the issue. I have checked transfer speed from the NAS device that holds the files to the computer running Duplicati and is higher 100MB/s. During backup operation RAM usage is <50%, CPU usage <20%.

I have observed that during backup, the network usage in outbound direction is not continuous, as if Duplicati only uploads content for a couple of minutes and then stops uploading for a couple of minutes. This plot shows upload network usage of the computer for a span of 5 minutes. No other software is running when backup is working.

This upload behavior is confirmed by ingress metric of Azure, which shows a similar pattern.

I’m executing Duplicate with the following command line instructions ( is the IP address of the NAS that holds de files to be backed up):

net use R: \\\Volume-1 <password> /user:***** /persistent:no
"C:\Program Files\Duplicati 2\Duplicati.CommandLine.exe" backup azure://** R:\ --parameters-file=DuplicatiParameters.txt --dbpath=mydb.sqlite --backup-name=Volum-1
net use R: /delete /yes

Contents of DuplicatiParameters.txt file:


I can’t find the reason why backup operations are so slow. Any help would be appreciated. Please advise if more information is needed.

… have you already experimented with file-size limit. You are using 50 MB dblock-size. I think it should be the same. So just try using 1 GB. I’d be interesting in your new chart how it will look like!

Are these 30 files the only files on the R: drive? If so, that removes potential scanning-for-files slowdown. Duplicati usually runs best with direct source access, as it reduces the scanning and reading overheads.

Do these files have scattered internal changes from backup to backup? You can estimate it from the log.
BytesUploaded in BackupStatistics in Complete log would be high, because deduplication gets low.

In addition to the idea from @MH484 (thanks!), increasing –blocksize might reduce block tracking work, however it can’t be changed without fresh backup start, i.e. manually delete Database and Azure backup. –dblock-size can be changed whenver you like, but changes do have some side-effects for Compacting.

Choosing sizes in Duplicati talks about this some, but best plan depends on the nature of the source files and restore needs. Duplicati backs up only changes in source files, using a fixed-boundary dedup design.

Worst-case for restore would be having to collect scattered changes from a time-series of backups. If the source is very different each backup, this means a big upload, but also little data gathering at restore time.

Even though you have a large –asynchronous-upload-limit, can you see if Temp folder is making use of it? The backup has the look of something that can’t get data from NAS fast enough, but cause of it is unclear.
Testing with the higher --dblock-size getting similar backup time (but more bursty) would support that idea.