Using Unison to sync two external USB drives

Unison will sync these two USB drives

I’m pretty impressed with this backup utility which I’m running on Ubuntu Intrepid.

It’s easily added via System > Add/Remove and then pretty easy to run.

I have two Western Digital Elements External Hard Drives (640Gigs per drive) and each disk is about half full.

The only warning about using this programme is that when you first do a sync it takes a LONG time!

It basically analyses each file to make a “hash” (a bit like a fingerprint) and large files take a long time to make a hash for! It took about 6 hours to create the hash files as it has to analyse both source AND destination disks.

You don’t get a “progress bar” but it tells you which file it is working on and this might not be in the same order as they appear in the directory as it analyses capitalised file names and directories first whereas the directory listing order is case insensitive.

After it had finished it flagged a lot of “permissions” differences so I selected “actions > resolve all conflicts in favour of first root” and this synced the file permissions.

The thing I really liked is that once the hash files had been built and you re-sync it again it’s VERY fast the next time as it only needs to analyse NEW files rather than all of them. It took just a few seconds rather than a few hours so the hashing is well worth the initial wait.