Remember my recent disk issues? As a side effect of protecting myself, I have a good example of deduplication results.
I have a second disk in my server, with slave Hammer PFSs to match what’s on my main disk. I hadn’t put them in fstab, so they weren’t getting mounted and updated. I got them re-created, but they were nearly full. Here’s an abbreviated df, from which you should be able to tell which drives I have :
Size Used Avail Capacity 929G 729G 200G 78% /slave/slavehome 929G 729G 200G 78% /slave/slavevar 929G 729G 200G 78% /slave/slaveusr 929G 729G 200G 78% /slave/slaveslash
That 78% is how full the Hammer volume was. I turned on Hammer deduplication, since it’s off by default. The very next day:
Size Used Avail Capacity 929G 612G 318G 66% /slave/slavehome 929G 612G 318G 66% /slave/slavevar 929G 612G 318G 66% /slave/slaveusr 929G 612G 318G 66% /slave/slaveslash
It’s a 1 terabyte disk, and I gained more than 10% back – That’s 100g of disk space that I gained overnight. There might be more tomorrow, given that it was all of 5 minutes of dedup work.
This won’t surprise you if you’ve seen previous deduplication links here, like my previous results or some real-world tests. It’s still great. I’d suggest turning it on if you haven’t – hammer viconfig the appropriate PFS and uncomment the dedup line.