FreeNAS or ZFSonLinux?

[Alan Milewczyk]

Not sure if this is the correct section of the forum but here goes....

I built a rubbishy FreeNAS system a few years back, following bad advice from Youtube videos and before I had read up about the Hardware requirements here. That system was subsequently repurposed as a general Linux Mint system but I'm now ready to do things properly. I've just posted in another part of the forum with my requirements and initial thoughts on a proposed system (https://forums.freenas.org/index.php?threads/new-build-doing-it-right-this-time.49473/).

However, I have some nagging doubts whether or not FreeNAS is the best solution for me. One option I'm considering is ZFSonLinux. What are the relative merits or otherwise of the two options? Although I tend towards FreeNAS, one attraction as I can see with ZFSonLinux is the flexibility in being able to add to a storage pool (I'm looking at the example near the bottom of http://www.howtogeek.com/175159/an-introduction-to-the-z-file-system-zfs-for-linux/). As I understand it, FreeNAS doesn't allow you to combine zpools into one contiguous storage pool. Or have I got this wrong?

If you feel this question is better handled in another part of the forum just let me know.

Thanks

Alan

 

[MrToddsFriends]

Although I tend towards FreeNAS, one attraction as I can see with ZFSonLinux is the flexibility in being able to add to a storage pool (I'm looking at the example near the bottom of http://www.howtogeek.com/175159/an-introduction-to-the-z-file-system-zfs-for-linux/). As I understand it, FreeNAS doesn't allow you to combine zpools into one contiguous storage pool. Or have I got this wrong?

That's not combining several pools into one but extending a pool by adding a vdev.
http://doc.freenas.org/9.10/storage.html#extending-a-zfs-volume

 

[Alan Milewczyk]

Thanks for the reply MrToddsFriends.

Can I clarify the position, please? To look at RAID solutions simply, what we are doing is combining a number of hard drives so that they look like one, with varying degrees of redundancy depending on the RAID solution adopted. I know that when I combine those 8 drives (64TB total) I should get approx 40TB usable space (with RAIDZ2), so that it looks like a 40TB volume (using Windows terminology) when I map it in a Windows system. I can create folders on that volume and keep adding files seamlessly into that volume into the existing folders.

I know that I can increase the size of "volume" by changing all 8TB drives over to 10TB (obviously following the correct procedures). But if instead I buy, say, another 4 hard drives, each of them 8TB I know that I cannot add them to the existing VDEV, so the only option is to create a new VDEV. If I go RAIDZ2, that should create around 20TB of newly usable space.

What I am trying to achieve is a situation where I can "combine" or "pool" (using those terms in a non-techie way) the original 40TB and the new 20TB into one contiguous/seamless space or "volume" of 60TB - so if I add new files into that "volume" I am doing it oblivious of the actual hardware makeup. My understanding is that FreeNAS doesn't won't let me do this, or have I got this wrong?

Thanks

Alan

 

[snaptec]

Sure FreeNAS allows you this.
Recommended is adding vdevs from the same type. If you have 8x8tb in z2, you can add another 8x8tb z2 vdev to the pool and double your space.

You can (but shouldn't...) have a 8x8tb z2 and add a single drive as vdev. When a single vdev dies (aka the single drive) your pool is lost


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[snaptec]

Sure FreeNAS allows you this.
Recommended is adding vdevs from the same type. If you have 8x8tb in z2, you can add another 8x8tb z2 vdev to the pool and double your space.

You can (but shouldn't...) have a 8x8tb z2 and add a single drive as vdev. When a single vdev dies (aka the single drive) your pool is lost


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[Alan Milewczyk]

Ah, thank you. An important misconception put right! And I understand why your single drive vdev example is bad practice.

Thanks

Alan

 

[Arwen]

Please note that ZFS on FreeNAS, FreeBSD, MacOS, Illuminos & Linux is more or
less the same version, and is portable between these OSes. Some features lag a bit
betweem them. But eventually get ported over. Sun / Oracle ZFS is different beginning
with Zpool version 29.

On the subject of ZFSonLinux, I have all my home Linux boxes using ZFS:

• Minature media server with a 1TB mSATA SSD + 2TB SATA HDD
• Desktop quad core AMD64 with 64GB SATA DOM + 500GB SATA HDD
• Small laptop with 1TB SATA SSD, (used BTRFS for 2 years until about a month ago)

Unfortunantly none support ECC memory. But, all have the OS part mirrored and the rest
un-mirrored. I'd rather have ZFS on non-ECC memory at present, than any other file system.
However, note that I have multiple, redundant backups in case non-ECC memory hoses one
of my Linux ZFS pools.

 

[GBillR]

Not sure if this is the correct section of the forum but here goes....
As I understand it, FreeNAS doesn't allow you to combine zpools into one contiguous storage pool. Or have I got this wrong?

I know you seem to have received your answer, but if you haven't already looked at Cyberjocks slideshow you should: https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

It explains the answer to your question, as well as much more.

 

[Robert Trevellyan]

What are the relative merits or otherwise of the two options?

If you want something that's intended to be treated as a storage appliance, FreeNAS is probably the better option. If you want a more conventional server where there are fewer constraints, but setup is more involved, ZFS on Linux might be the way to go. In the latter case, Ubuntu Server is a particularly convenient option because it now ships with ZFS.

 

[wblock]

If you want a stable, tested ZFS that has been used in production for years, pick FreeNAS or FreeBSD. ZFS on Linux is still very young.

 

[Alan Milewczyk]

Apologies for the delay in responding and thank you to all who replied. I'm still at the drawing board stage weighing up the alternatives.

 

[scwst]

I'm late to the party, but have just moved my /home folder on the main family Ubuntu Gnome machine to ZFS after getting hooked on the file system with my FreeNAS box. After a few days setting various things up, my suggestion would be:

- If this is just for storage, use FreeNAS. The GUI tools are far superior to what is (currently) available on Linux, especially when it comes to regular snapshots and their management. Also, FreeNAS is based on FreeBSD, which is far slower to support new hardware, but rock-stable, and has included ZFS for far longer.

- If you need the computer for other things as well, however, seriously consider Ubuntu. For instance, in my case, I have three users, and systemd has made multiseat setups trivial on Linux, which saves serious hardware money. Also, there is no Steam for FreeBSD that I am aware of. Note that at time of writing, booting off of ZFS on Ubuntu is still something of a pain, but I just use a small SSD for root.

 

[Stux]

ZFS on both systems will be more or less the same. You will lose the ease of setup, maintenance and configuration with a Linux setup but you will gain the ability to run docker containers on the main kernel without a VM, and any other Linuxy things.

It is possible to run Linux (and thus docker) in a VM on FreeNAS.

 

[Arwen]

One thing I missed with ZFSonLinux is easy administration of ABEs, (Alternate Boot Environments). Solaris 11
has it perfect, and Solaris 10 is not too bad. Beginning with FreeNAS 9.3 we get ABEs, (with management).

But Linux, while you can manually generate ABEs using ZFS snapshots & clones, there are no tools to simplify
managing ZFS ABEs. I have since written a script that helps ALOT with making, destroying, listing and verifying
ABEs. It's not perfect or feature complete, but it does work. I doubt I will publish the script because it is very
environment specific.

 

[scwst]

Give it time. I wouldn't be surprised at all if the Ubuntu people came out with a GUI administration tool for ZFS, given how they're pushing it (and it's not like they are all busy with Mir and Unity anymore).

 

[Arwen]

Give it time. I wouldn't be surprised at all if the Ubuntu people came out with a GUI administration tool for ZFS, given how they're pushing it (and it's not like they are all busy with Mir and Unity anymore).

Perhaps. But, without an install option for root on ZFS, many people will continue to use stock Linux FSes for root. Thus, no need manage ZFS alternate boot environments.

 

[Robert Trevellyan]

you will gain the ability to run docker containers on the main kernel without a VM

And LXD, don't forget LXD.

 

[scwst]

So here is an interesting technical difference I wasn't aware of until now: It seems that ZFS on Linux is guilty of double caching. I've been reading William Speirs' ZFS on Linux. Internals and Administration, and on page 39/40, there is a (far too) brief introduction to the ARC and a (short) intro to Linux' LRU 2Q cache policy. This quote follows:

Unfortunately, this causes double-caching when ZFS is used on Linux. Data is cached both in the Linux page cache, and in ZFS's ARC. While the performance impact is minimal, it can greatly increase the amount of memory used by the system. Although it is not possible to disable Linux's page cache, it is possible to tune ZFS's ARC to prevent much of this double caching.

Note that in 2013, this subject came up on the ZFS Discuss mailing list at http://list.zfsonlinux.org/pipermail/zfs-discuss/2013-October/011490.html and we have this:

The Linux VFS permits the filesystem to decide when and when not to use the page cache. Currently, double caching only occurs when doing mmap() on datasets, which is something that we inherited from Solaris. Regular file operations on ZFS datasets will be cached exclusively in ARC.

It seems that this is scheduled to being taken care of in 0.7.0 (whenever that will be): http://wiki.opensfs.org/images/d/da/OpenZFS_on_Linux_Development_LDM14.pdf - as far as I can tell, we are at 0.6.5.9 (https://github.com/zfsonlinux/zfs/releases).