I've stumbled upon this post detailing a user's experience and testing with ZFS (both array and pools) on Unraid. Anecdotally, I also often read about disappointing and unusually slow ZFS performance on Unraid, as compared to BTRFS. Even with NVMe pools where performance should be no issue whatsoever. I understand ZFS on the Unraid array is a special (and discouraged) use case, but pools should not be affected afaik.

Personally, I've always stuck with BTRFS, but I am getting tired of the lack of proper GUI/native systems in Unraid to manage snapshots. So I've been itching to give ZFS a try, to see if the snapshot experience was any better; but these experiences have been putting me off. Reading into them however, no one seems to give a concrete explanation as to why ZFS pool performance is so poor in Unraid.

Could someone more technically minded than me comment on this, and hopefully give an explanation?

There's known issue with ZFS on the array; pools are not affected, except if you use user shares, with Unraid that goes through FUSE, and it will always have some overhead, but if you use a disk share or make the share exclusive, pool performance should be the same as any other OS with ZFS, and it is for me compared to TrueNAS for example.

45 minutes ago, JorgeB said:

There's known issue with ZFS on the array

Yeah, I never planned to use ZFS on the array, since single disk parity and individual disk spinup was the whole reason I chose Unraid. If I ever need a ZFS HDD server, I'll either run it in pools or just use TrueNAS.

46 minutes ago, JorgeB said:

make the share exclusive

I have a side question regarding that. I'm not quite sure I understood the Unraid documentation regarding exclusive shares. Does it mean:

1. /mnt/user/data becomes identical to /mnt/pool/data and both can be used interchangeably?

2. /mnt/pool/data becomes the default option?

I ask, because when installing new dockers after enabling exclusive shares, the default paths seem to randomly alternate between /mnt/user/... and /mnt/pool/...

50 minutes ago, JorgeB said:

should be the same as any other OS with ZFS

That's good to hear from you over anyone else. Were there any significant ZFS changes between 7.0 (the version the user in that post is running) and 7.1.4? Because if not I still can't explain what causes the orders of magnitude slower speeds of ZFS compared to BTRFS in that post. One one hand, he's running 32GB of RAM, and I assume he had enough free for ARC. His screenshots indicate he's using direct paths to pools, skipping FUSE overhead. On the other he's not really running a clean test since he's comparing a BTRFS RAID1 of 2 different drives, with a single disk ZFS pool of yet another drive model.

The obvious answer is to test for myself, but I just don't have the spare hardware or server downtime to test for myself. Quality resources on ZFS vs BTRFS in pools on Unraid specifically are pretty much nonexistent. The Unraid documentation does a good job explaining the different file systems, but is still very surface level with no performance comparisons; and advertising snapshot support when there's still no built in snapshot tools (afaik) in Unraid is a bit disingenuous. The Snapshot plugin for BTRFS hasn't been updated in 2 years either, which only leaves btrbk and good old elbow grease.

Do you have any opinion or experience you'd like to share on ZFS vs BTRFS for Unraid pools? BTRFS has worked fine so far, but the snapshot experience is not great. I'm about to get into some database-heavy stuff with critical data, so I'd like to commit to a file system before I start setting all that up.

43 minutes ago, SinoBreizh said:

/mnt/user/data becomes identical to /mnt/pool/data and both can be used interchangeably?

Correct.

43 minutes ago, SinoBreizh said:

/mnt/pool/data becomes the default option?

Independent of using /mnt/user or /mnt/pool it will always bypass FUSE

44 minutes ago, SinoBreizh said:

Do you have any opinion or experience you'd like to share on ZFS vs BTRFS for Unraid pools? BTRFS has worked fine so far, but the snapshot experience is not great. I'm about to get into some database-heavy stuff with critical data, so I'd like to commit to a file system before I start setting all that up.

I use both. Btrfs has some advantages, mainly regarding flexibility. I find performance to be very similar between both for similarly configured pools, except mirrors, where ZFS stripes them for reads, and Btrfs doesn't, so it has a performance benefit there.