I'm planning on building my first NAS box and currently I'm considering FreeNAS and ZFS for it. I read up on ZFS and it's feature set sounds interesting, although I will probably only use a fraction of it.
Most guides say that the recommended rule of thumb is that you need 1 GB of (ECC-)RAM for every TB of disk space in your pool. So my question is, what is the actual (expected) impact on ignoring this rule?
Here is a setup of someone who build a 71 TiB NAS with ZFS and 16GB RAM. According to him it run's like a charm. He uses Linux however (if this makes a difference).
So apparently you don't actually need 96 or even 64 Gigs of RAM to run such a large pool. But the rule must be there for a reason. So what happens if you do not have the recommended amount of RAM? Is it just a bit slower or do you run the risk of losing data or accessing your data at a snails pace only?
I realize that this has also a lot to do with the features that will be used, so here are the parameters I'm considering:
- It's a home system
- 16GB ECC RAM (the maximum supported by the setup I have in mind)
- No deduplication, no ZIL, no L2ARC
- Probably with compression enabled
- Will store mostly media files of various sizes
- Will probably run bit torrent or similar services (frequent smaller reads/writes)
- 4 disks, probably 5 TB each
- Actual pool setup will probably be part of another question but I think no RAIDZ (although I would be interested to know if it actually makes a difference in this context), probably two pools with two disks each (for 10TB netto storage), one acting as backup