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> In all honesty I can't understand why would anyone use anything other than zfs nowadays for important data. In datacenters many probably do, however most hom

> In all honesty I can't understand why would anyone use anything other than zfs nowadays for important data. In datacenters many probably do, however most home/soho NAS machines are severely limited wrt memory and CPU power, which could be a limit. My self assembled NAS uses a Atom board to keep power requirements low since it stays always on, and I can't complain about its performance, however that CPU doesn't support more than 4GB RAM which is considered the minimum to properly use ZFS (NAS4free). Many cheap commercial NAS boxes used in small offices are even more limited. I wonder if there are any technical reasons preventing ZFS to operate (or be adapted to) in low memory environments.

Wowfunhappy 6y ago
I have used ZFS with 1 GB of RAM. It worked fine, it just wasn’t able to cache stuff to memory.
amarshall 6y ago
> 4GB RAM which is considered the minimum to properly use ZFS This is mostly a myth with origins in the high-memory requirements of ZFS deduplication (which few should use, anyway). Of course, more memory allows for more caching, but that’s true of any filesystem on a “modern” OS.
- djsumdog 6y ago
  Yea I only have 4GB of ram on my little HP MicroServer I use as a NAS with ZFS. The only issues I seem to have is that ZFS encryption seems to use more CPU than luks encryption, but it's still not too bad (the AMD Turion(tm) II Neo on it doesn't have AES instructions). I might upgrade it to something with a better processor because I do want to run de-duplication on my 14TB drive at some point.
linsomniac 6y ago
I wonder if it would be useful to have a Optane for the memory-hungry portions of ZFS, particularly the dedup tables, especially to be able to run it on very small, efficient machines. My work backup server has "only" 32GB of RAM which is nowhere near enough to do dedup, even though there's a ton of stuff that could be deduplicated. Looks like it needs at least 64GB RAM to dedup, and that machine is maxed out. But at home I'm in a similar situation to the parent. I'd like to set up a NAS, but I use it mostly for backups long term storage and don't want a big machine sitting idle all the time. A tiny Atom with Optane for cache and DDT might be ideal, in my thinking. But for most of the storage use Backblaze is probably the right answer.
- Rafuino 6y ago
  Would the Optane in this case be used as an L2ARC to handle part or all of the dedupe table? I'm trying to brush up on my ZFS terminology at the moment...
  - linsomniac 6y ago
    Currently, AFAIK, the dedup table (DDT) has to reside entirely in RAM. The L2ARC is a disk-based cache of filesystem blocks (a pretty clever design, worth reading up on), but a very different thing from the DDT. You could definitely put the L2ARC on Optane, but Optane is probably better suited to the ZIL (ZFS Intent Log, basically the journal so writes can be quickly acked) if you aren't using literal NVRAM. Breaking the DDT out so it could exist on a Optane isn't currently available (again, AFAIK, but I recall hearing about some changes in that department, I don't recall specifics and may be misremembering). I've basically never had a machine big enough to comfortably use dedup except on trivial loads. My backup boxes, where I'd really like to use it, have all fallen over when enabling dedup because of the RAM requirements.
    - fomine3 6y ago
      ZFS 0.8 supports a feature called "Allocation Class" that makes DDT able to working on "special" storage device (aimed to use NVMe) rather than RAM. It also supports to put metadata and small blocks on special device. https://forums.servethehome.com/index.php?threads/zfs-allocation-classes-performance-benchmarks.26111/ https://forums.servethehome.com/index.php?threads/zfs-alloca...
znpy 6y ago
I've been running zfs on a 2gb machine with little I/O (it mostly receives snapshots) and had no issue so far. Generally speaking, I will go with lower specs machines until I run into some actual problem. Haven't so far.

Wowfunhappy 6y ago

I have used ZFS with 1 GB of RAM. It worked fine, it just wasn’t able to cache stuff to memory.

amarshall 6y ago

> 4GB RAM which is considered the minimum to properly use ZFS This is mostly a myth with origins in the high-memory requirements of ZFS deduplication (which few should use, anyway). Of course, more memory allows for more caching, but that’s true of any filesystem on a “modern” OS.

djsumdog 6y ago
Yea I only have 4GB of ram on my little HP MicroServer I use as a NAS with ZFS. The only issues I seem to have is that ZFS encryption seems to use more CPU than luks encryption, but it's still not too bad (the AMD Turion(tm) II Neo on it doesn't have AES instructions). I might upgrade it to something with a better processor because I do want to run de-duplication on my 14TB drive at some point.

linsomniac 6y ago

I wonder if it would be useful to have a Optane for the memory-hungry portions of ZFS, particularly the dedup tables, especially to be able to run it on very small, efficient machines. My work backup server has "only" 32GB of RAM which is nowhere near enough to do dedup, even though there's a ton of stuff that could be deduplicated. Looks like it needs at least 64GB RAM to dedup, and that machine is maxed out. But at home I'm in a similar situation to the parent. I'd like to set up a NAS, but I use it mostly for backups long term storage and don't want a big machine sitting idle all the time. A tiny Atom with Optane for cache and DDT might be ideal, in my thinking. But for most of the storage use Backblaze is probably the right answer.

Rafuino 6y ago
Would the Optane in this case be used as an L2ARC to handle part or all of the dedupe table? I'm trying to brush up on my ZFS terminology at the moment...
- linsomniac 6y ago
  Currently, AFAIK, the dedup table (DDT) has to reside entirely in RAM. The L2ARC is a disk-based cache of filesystem blocks (a pretty clever design, worth reading up on), but a very different thing from the DDT. You could definitely put the L2ARC on Optane, but Optane is probably better suited to the ZIL (ZFS Intent Log, basically the journal so writes can be quickly acked) if you aren't using literal NVRAM. Breaking the DDT out so it could exist on a Optane isn't currently available (again, AFAIK, but I recall hearing about some changes in that department, I don't recall specifics and may be misremembering). I've basically never had a machine big enough to comfortably use dedup except on trivial loads. My backup boxes, where I'd really like to use it, have all fallen over when enabling dedup because of the RAM requirements.
  - fomine3 6y ago
    ZFS 0.8 supports a feature called "Allocation Class" that makes DDT able to working on "special" storage device (aimed to use NVMe) rather than RAM. It also supports to put metadata and small blocks on special device. https://forums.servethehome.com/index.php?threads/zfs-allocation-classes-performance-benchmarks.26111/ https://forums.servethehome.com/index.php?threads/zfs-alloca...

znpy 6y ago

I've been running zfs on a 2gb machine with little I/O (it mostly receives snapshots) and had no issue so far. Generally speaking, I will go with lower specs machines until I run into some actual problem. Haven't so far.