How much RAM for ZFS? (different Recommended System Requirements)

[VGBH]

The Recommended System Requirements are confusing because they are different.
For context, I will use 6 x 3840GB SSD´s.
RAIDZ type: RAIDz2
After calculating with RAIDZ Calculator I can use 15360 GB.
At the moment, I will use ~10 TB used storage.
The New System will have 512 GB RAM in each Node and 64 GB RAM in Backup Server.

PVE Recommended System Requirements

For Ceph and ZFS, additional memory is required; approximately 1GB of memory for every TB of used storage.

I need + 10 GB more RAM.


PVE ZFS Performance Tips

ZFS works best with a lot of memory. If you intend to use ZFS make sure to have enough RAM available for it. A good calculation is 4GB plus 1GB RAM for each TBRAW disk space.

I need +75 GB more RAM.


Which calculation is right?

 

[shanreich]

With the second calculation I'd get ~20 GB, not 75, since 4 + (1 * 15) = 19.

In newer installations we limit the maximum amount of ARC to 16 GiB, so I'd recommend sticking with that and see how your system performs. Generally ZFS performs better the more memory you give to it, but of course there are diminishing returns with increasing storage size.

I'll look into improving the documentation to be more consistent with regards to the recommended storage.