3 vs 5 drive vdev

[KMR]

Hello,

I have just completed my first FreeNAS box from old components I had laying around; it has the following specs:

Intel E8400 CPU at 3.0GHz (Socket 775)
Gigabyte Motherboard (supports 16GB ram)
12GB G.Skill RAM (I will upgrade to 16GB when I need to)
550W Cooler Master PSU
3x 3TB Seagate HDDs.

I am quite happy with the build thus far; the speeds are good and I have the active directory permissions working reasonably well. I created a 3 disk vdev in RAIDZ1 for a total of 5.2TB usable storage. I was wondering if I should bite the bullet and buy two more drives now and rebuild the pool with a 5 disk Vdev (my wife won't be happy about this). Eventually my storage requirements will surpass the 5.2TB and I'll need to expand the pool with another Vdev. If I keep my current configuration I will need to either add another 3 disk Vdev or rebuild the full array later on as a 5 disk Vdev. Rebuilding the pool later on when it is almost full will be much more time consuming as I have a copy of all my files on a (almost full) 3TB WD Green drive now.

So, in my situation:
Are 5 disk vdev's that much better than 3 disk vdev's to warrant the extra expenditure now (and possible wife wrath)?
Should I buy two more disks and rebuild the pool now as a 5 disk vdev when it is easier, or rebuild it as a 5 disk vdev later on?
Or, should I leave the 3 disk vdev and just add another 3 disk vdev when I need the extra storage?

Thanks!

 

[paleoN]

I created a 3 disk vdev in RAIDZ1 for a total of 5.2TB usable storage. I was wondering if I should bite the bullet and buy two more drives now and rebuild the pool with a 5 disk Vdev (my wife won't be happy about this). Eventually my storage requirements will surpass the 5.2TB and I'll need to expand the pool with another Vdev.

Buy three more, plus a nice gift ;), and create a 6 x disk raidz2 pool.

Are 5 disk vdev's that much better than 3 disk vdev's to warrant the extra expenditure now (and possible wife wrath)?

5 x disk raidz1 is worse with 3TB drives. I wouldn't even run a 3 x disk raidz1 with 3TB drives. Go double-parity, raidz2.

 

[KMR]

Is there some reason for that? I have heard that raidz2 is slower than raidz1, but I could deal with that if there was good reason. However, I'm not sure I would be able to get away with buying another three drives.

Thanks for your input!

P.S. I suppose I should mention that I have a 3TB WD Green sitting on a shelf and a 3TB WD Green as my old server drive so I am able to use both of those drives for backup now. I don't really want to use raid as a backup solution.. there is too much that can go wrong.

 

[survive]

Hi KMR,

The reason we like to push raidz2 over raidz gets down to reliability during a rebuild.

There is noting (usually) that will stress your disk subsystem than a rebuild, and a rebuild on a reasonably full 3TB-based vdev can take many hours (days even) of your disks running full-bore. If there is anytime that another disk will fail, this will be it, at which point all your data is toast.

Raidz2 is slower than raidz given the same number of disks, sure.....the thing to really worry about is does it slow it down enough to matter. In my case I lost ~40MB/s going from raidz to raidz2, from ~480MB/s in the primitive "dd" test to around 440MB/s. Didn't bother me one bit given that's almost 4 times what I could ever move over gig-e.

note: 6 disks is one of the "ideal" raidz2 configurations.

-Will

 

[KMR]

That is great information. Thank you.

So if I built a 6 disk raidz2 vdev I would have about 10TB usable storage and I would need to add vdevs in 6 disk increments. I may have to wait a while before buying so I can figure out how to explain that large a purchase on hard drives.

Is there anything else that I should consider? Such as staggered hard drive spin ups or power supply improvements?

 

[survive]

Hi KMR,

If your BIOS supports staggered spinup there's certainly no reason not to use it. That's about the only place you can set such a thing.

As far as the PSU goes I would probably consider going with something other than Cooler Master. Keep in mind I'm a bit of a hardware snob, so I tend to recommend Corsair, Antec and (my particular favorite) Seasonic. Keep in mind you don't have to go big, but you do want to go quality.

Take a look at this post:

http://forums.freenas.org/showthread.php?6273-PSU-sizing-for-home-file-server&highlight=power+supply

I would think this:

http://www.newegg.com/Product/Product.aspx?Item=N82E16817151124

would be perfectly fine for your application.

-Will

 

[paleoN]

I don't really want to use raid as a backup solution.. there is too much that can go wrong.

Good, it isn't.

So if I built a 6 disk raidz2 vdev I would have about 10TB usable storage and I would need to add vdevs in 6 disk increments. I may have to wait a while before buying so I can figure out how to explain that large a purchase on hard drives.

SWMBO aside, you're much better off building it properly from the start. Don't forget you can also replace the existing disks with larger ones to grow the pool.

What are your storage requirements over the next few years? I assumed ≈10TB would see you through given what you were starting with. What case are you using, how many drive bays does it have, etc. Plan out your fully built configuration and work backwards. Making sure to plan any and all upgrades carefully.