Whats the best volume size for backups to external hard drive

I’m using the default volume size (50 MB) for my backup of about 500 GB to external hard drive, resulting in about 17 000 files in my duplicati folder. Backup takes about 1.5 hours (also impacted by slow USB 2 speed on the computer), a test restore took several days. Should I choose a different size for this scenario?

What is the best block size (Thinking of restore time) for a Dropbox backup? mentions 200-300 MB for dropbox so I guess I could at least use the same for my hard drive backup or what do you think?

Best Regards


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i use 250MB whan backing up to my NAS (probably slower than your USB2). i see a significant increase in restore performance from when i started using the default 50MB.

And I use 1 GB file-size limit. How ever I decided to use this because of file-size limit of some cloud services, which allow max. size between 1 to 4 GB mostly. With 1 GB I know I can upload to most everywhere. Local processing of backup and restore is quick.

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Local disk is one of the cases where the size matters very little. I’m using everything between 8 MB to 4 GB with local disks. What’s the key difference? Key difference is that with 8 MB blocks, it’s possible to delete whole file without running compact. Yet if the backup size is pretty small and disk speed is good. It really doesn’t matter what kind of block size you’re using.

When I’m using large blocks? With fast disks, and huge static files. So even if block size is 4 GB it still allows reasonable data deletion without compact. But when the compact runs, it’s lots of disk traffic. But again, with local disks that doesn’t matter. If the destination would be remote, I would probably drop size considerably to shorten time (and network traffic) required for compaction.

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Thank you very much! I’ll increase the size then and see what kind of changes I get in regards to backup speed.

I use a 1Gb file size for local backups. You’d probably want to go smaller than that if confined to USB 2 speeds otherwise compacts, verifies, and restores of (eg) single files will get rather slow, but more than 50Mb is definitely OK :slight_smile:

I’ve increased the size to 250 MB and the first backup afterwards was ok from performance point of view but the second one now is stuck in the “Deleting unwanted files” phase for over a day now already ("Deleting unwanted files" takes ages. Duplicati busy since 5 days. · Issue #1582 · duplicati/duplicati · GitHub) But I guess I’ll just have to keep it running for a couple of days now.