Choosing a RAID level

[richardb]

Hey all, I am building a new NAS system using FreeNAS 8 from a Mini ITX system. I was wondering what RAID level might make sense. The specifics of this are:

- The system is running on a Intel Atom processor with 4GB of RAM on a Jetway MiniITX board with 6 SATA ports.
- I am starting with 6x500GB drives, but will be replacing them with larger drives at some point in the near future, so ease of upgrading will be important.
- The primary requirement is that the data survives drive crashes and the like, not speed.

Any thoughts?

 

[ProtoSD]

Hi Richardb,

Welcome to the FreeNAS 8 forums. If you haven't taken the time yet, have a look at the documentation, FAQs, and videos available at this thread:

FAQS-Documentation-are-HERE

You basically have the same hardware I do with smaller drives. I have a 5 disk raidz2, with one open port for a cold spare or in case I need to hook up a disk and copy stuff off. With the raidz2 you'll have the ability to have ANY 2 disks fail at the same time and still have access to your files. I had one disk fail and ran just fine until the replacement arrived and it was nice having the knowledge that my files still had that extra redundancy left and I could access everything too. Like you, speed isn't an issue for me, more the redundancy. At some point I'll probably play a little more to see what speed I can get. Right now the current version of ZFS doesn't allow you to set the 'autoexpand', so even if you replace each of your drives one at a time and let them resilver, you won't be able to expand your pool to get the extra space. Plan carefully, it can be a hassle to copy everything off so you can rebuild with bigger drives. I decided to switch from z1 to z2 and had to empty everything off and rebuild my pool.

 

[matthewowen01]

raidz2. you get 2 drives of redundancy and the rest are data (math mathematically speaking).

 

[richardb]

Hm, RaidZ2 is the winner so far, but I am concerned about the expandability. With other RAID levels, I can expand the array by replacing drives one by one and rebuilding. I can't do that with RAIDZ2?

 

[ProtoSD]

You can, just not with the version of ZFS that FreeNAS uses currently. It could *possibly* be this time next year and that could change. That's just a guess, but....

You could yank one of the drives from your z2 array, have 2 open slots, backup your stuff to 2 3GB drives, and then replace them all.

I'm filling my NAS a lot faster than I thought, so give yourself some room and start with some bigger disks. Then when you're ready to expand there'll hopefully be a newer version of ZFS.

 

[ProtoSD]

You can, just not with the version of ZFS that FreeNAS uses currently. It could *possibly* be this time next year and that could change. That's just a guess, but....

You could yank one of the drives from your z2 array, have 2 open slots, backup your stuff to 2 3GB drives, and then replace them all.

I'm filling my NAS a lot faster than I thought, so give yourself some room and start with some bigger disks. Then when you're ready to expand there'll hopefully be a newer version of ZFS.

 

[matthewowen01]

well i love being wrong (really i do) it is entirely possible to expand a vdev by replacing disks one by one and allowing it to resilver in between, the added space cannot be used until the pool is exported and re imported, that's the auto expand property I've been speaking of.

http://forums.freenas.org/showthread.php?1661-expanding-controllers&p=7798&viewfull=1#post7798

 

[richardb]

well i love being wrong (really i do) it is entirely possible to expand a vdev by replacing disks one by one and allowing it to resilver in between

Interesting, but I am not sure I would trust it with important data on the basis of that until it has been a little more widely tested. (not that I am going to do anything without a decent backup as well, of course... :)).

Still, looks like a Raidz2 is the way to go for me, but I might hold off on using this server fully until I have all of the larger discs available. Thanks everyone for your help!

 

[matthewowen01]

i've done it many times before with the newer version, the only change is the need to export and import it, which silly me forgot to do.