ZFS Raid Mirror - RAM Requirement, is it really that high?

[Innocuous]

Hi all,

I am thinking of building my first FreeNAS server for home use. I have 6TB of data (mainly video media) which I am thinking in running in a Raid 1 (Mirror) configuration - so 12TB of disks. When I say mirror, I want to be clear it will be a pure Raid 1 (Mirror) with 2x 3TB drives, 2X2TB & 2x 1TB drives forming separate file repositories (I don't feel the need to use Raid 1+0 as I believe it introduces additional risk to me for little benefit).

I have read everywhere that ZFS has high RAM requirements and that it can be CPU intensive. From my reasonable knowledge of PC's though I would have thought that the requirement of the CPU and RAM would be significantly less with a Raid 1 mirror configuration than that of Raid Z1/2/3 as the required processing and checking would require significantly less calculation, however I cant find any posts or discussion related to this? Is this true or am I missing something that ZFS is doing which requires greater RAM / CPU requirements?

I will also want to run SabNZBD, SickBeard, CrashPlan and maybe even Plex. So I guess upping my RAM a bit from the Spec below would be useful, it is the scale of the increase that I am most concerned with. So how much RAM would you guys recommend on such as set-up?

The hardware I am thinking of re-purposing is as follows:
AMD Athlon II X2 265
6GB DDR3
ASUS M4A785TD-V EVO motherboard
SIL 3114 SATA Controller (JBOD Config)

Thanks all,

Jon

 

[cyberjock]

I have read everywhere that ZFS has high RAM requirements and that it can be CPU intensive. From my reasonable knowledge of PC's though I would have thought that the requirement of the CPU and RAM would be significantly less with a Raid 1 mirror configuration than that of Raid Z1/2/3 as the required processing and checking would require significantly less calculation, however I cant find any posts or discussion related to this? Is this true or am I missing something that ZFS is doing which requires greater RAM / CPU requirements?

Nope. Still need 8GB minimum like the manual says. You may need more because of multiple pools. So don't buy 4x2GB sticks and hope it will work. You might end up disappointed.

 

[Innocuous]

Hmm that is interesting, what is all that RAM likely used for in this scenario then? I ask as I am now wondering if ZFS is the most effective technology for me to use. Maybe straight forward Raid 1 or Fake Raid 1 would be better suited to my needs.

 

[jgreco]

This is 2013, not 2005. 8GB is no longer a ton of RAM. FreeNAS comes configured to work well on modern systems with 8GB to 128GB and beyond, but some of those tuning choices make FreeNAS not fit well in smaller RAM configs.

If you wish to run your 2000 vintage Pentium III as a NAS, FreeNAS is not a good choice. There are plenty of alternatives aimed at smaller systems.

 

[Bobby]

Take this for what you want but don't yell at me if your data gets borked. I almost feel bad to post this as I don't want to encourage others to use in production. I'm sure I'll get trolled but here's my experience.

BACK UP YOUR DATA!!

I'm running 2 freenas 8.3.1 64bit boxes at different locations.

Box A
AMD dual core 7750 cpu
3 gig ram (yes 3 gigs)
3 x 3TB drives in zfs

It was running 24/7 for just under 3 months until the power went off last weekend. The older ups battery didn't work. Drives came back online no issue. Its hosting media for a plex server (on different machine) and 5-7 .VHDX files for hyper-v machines. So it gets decently constant use. The reporting shows the cpu is mostly bored but the ram is used up.

Box B
same as above but with 7g ram
running 24/7 for 20 days so far. hosting 10+ .vhdx files for hyper-v machines.

They r-sync to each other at night via internet as they are in different states. I did try using a beefy 32-bit box for zfs and it failed big time. Box A started out as a testing/learning machine. Next thing I knew I had kept putting stuff on it to where I didn't want to take it offline. I knew about the 8gig minimum requirement but the damn thing just kept working. Who knows how many issues I'll have if something starts to go wrong, but for now its running. If its for your personal stuff that you have backed up and want to learn about Freenas (possibly the hard way) sure go for it. If you're putting at a clients business, exceed the minimums. Used servers are crazy cheap on eBay.

 

[jgreco]

Actually I'm pretty sure that no one here will be too critical. As long as you understand the risks and have chosen a risk level that is comfortable to you based on a correct understanding, and you have backups, and you're prepared to cope with problems, well, then, great I think generally the participants respect anyone who's a big boy and who has bothered to read and comprehend. We may still point out things we think you may not be aware of, but that's not a level I consider to be crititicism. We learn through failure as well as success.

The situation we don't want is someone coming in and putting their precious data on a ZFS system built out of 8 external USB drives and a 4GB Pentium 4 laptop "because it was all they had available." And then running into a failure. Precious data combined with catastrophic failure results in tears. We hate tears. As you note, used servers, crazy cheap, exceed the minimums, etc., no good reason for tears.

Welcome aboard.