ZFS array on an underspecced system

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New Member
Nov 6, 2013
Hi everyone,

I have a rather old system (2009) lying idle around and figured I might make it more useful by adding NAS functionality to it. It runs a 64bit 6.0 RedHat Linux variant and the specs are quite old for these times: An Athlon2 X2 and 8 GB DDR2 800 MHz RAM. Thats the MB's max capacity, so anything requiring more than that would mandate a motherboard upgrade and obviously some new RAM sticks too.

It does however have quite a few SATA ports and I'm wondering how far could I go with a ZFS pool added in without having to upgrade most of the components in the system.

From the start I should say that the pool should be used mostly for storage so no read/write intensive activities are envisioned. Concurrent access is estimated to 1-2 users at a time and the files (mostly backups) would be accessed through ethernet connections (100 Mbps). High transfer speed is not a requirement as long as it doesn't drop under 10 Mpbs. Optionally a SAMBA service would run on the host system to facilitate access.

I want to strech things a little bit by grouping 3 x 3 TB disks into a RAID-Z array which should give me around 5.5 TB of usable storage. In addition a "normal" hdd (~1TB) would serve as the system and applications disk.

According to references on the web, such as this one from FreeBSD (20.2. The Z File System (ZFS)) 1GB per 1TB of storage is recommended, however it's not clear to me if it refers to usable storage (5.5 TB and 8GB RAM should be fine) or raw storage (a bit south of 9TB which goes over the recommended values). I've also read that people have managed to run ZFS pools on less than the recommended specs without running into issues as long as their read/write requirements were modest. It's also sometimes noted that the recommendations are more to the best practices type rather then mandatory.

I'm also rather familiar with another NAS system (N40L) also using a RAID-Z array (in budget at 8GB RAM) and I have noticed (via the free command) that the memory shows most of the time as available (7/8 capacity) when idle and doesn't drop under 4 GB when disks transfers (either to or from the array) take place. Again, this is also a low usage system.

I guess all I'm wondering about is whether the filesystem would crash and burn on an underspecced system or the the worst I could axpect is a performance penalty - I would prefer to avoid any crashes and/or data loss.

Oh, and I might also squeeze an always-on virtual machine on the same system, but this would get less or at most max 1GB RAM and would run off the system disk.

What do you guys think?


New Member
Jul 14, 2013
Personally, I also run linux (CentOS 6.x) since I know that a WHOLE lot better than any of the BSD variants. I prefer to stay as close to native as I can, so I decided to go with software raid using mdadm+LVM as opposed to ZFS. It doesn't have the pool scrubbing to protect against bit rot, but hardware requirements are MUCH more modest, and I've found it's also much more flexible (i.e. I can grow the array by a single disk)


Jul 23, 2013
Halifax NS
As long as you do *not* turn on dedup you should be fine. I run a ZFS on a HP microserver with 4 GB or RAM, with absolutely no issues. ( currently a 3x2 TB RAIDZ1)

The RAM recommendations on the web are for dedup . Stay away from dedup, it requires much more "muscle" than your ancient machine and generally makes a mess of things for ZFS neophytes and is unlikely to help in your use-case.

Do enable compression. With 100Mb ethernet you'll not notice the extra CPU load. Whether you wish a nicely wrapped system like Napp-It or Freenas or a roll your own like Linux ZOL, is a matter of preference; command line maintenance of ZFS is pretty easy and quickly learned.

One great feature of ZFS that new users do not use enough, is to create test pools with file backing. Then have your merry way the pool; learn the commands; see what happens; then chuck the pool away, no tears, no fuss.

Both RPM and DEB based packages are available. ZOL does seem to play nicer with 3.x kernels than with 2.6 ones. I would stick with Linux unless you have a SYS V Unix background ( solarisish OSs) or BSD experience. Learning either, while "fun " will get in the way of learning about ZFS.

My two cents.. ( except in the cold white north with no pennies, its rounded down to 0 )


New Member
Nov 6, 2013
Thank you all for your replies and useful feedback.

@OBasel yes, I'm planning on using ZFS on Linux: I have tried it before on a Debian based system and looked preety good

@phroenips It's most likely that the terminology and command lines are similar when using mdadm but since I started with ZFS I will keep mdadm learning in the queue for now

@ColdCanuck I just took a look at the RAM recommendations for dedup and the quoted 5 GB ! per 1 TB of storage (also in the FreeBSD link above) go significantly beyond my planned budget. I actually had the chance to exercise the ZFS command line on the other system I mentioned (the N40L): I also found it extremely easy to use and informative. I usually use a virtual machine with virtual disks to play around with the ZFS commands I'm unsure of.

Once again, thank you all for your help