5-disk ZFS; RAIDZ1 or RAIDZ3?

[par]

In the wiki it says start RAIDZ1 or RAIDZ3 at 5 disks. How much usable space will I have with each from 5x 4TB drives?

Does RAIDZ3 imply 3 parity drives? I guess that would be excessive. Why is RAIDZ2 not recommended for 5 disks, just the usable space vs parity ratio does not work in its favor?

I plan to run RAIDZ1 but am looking to understand this further, I have not been able to find much more detailed information on this situation.

 

[warri]

Yes, RaidZ3 implies 3 "parity" drives. You can use a Z2 on 5 disks without problems, but you might encounter some performance penalty - I think it has been discussed somewhere in this forum already.

 

[par]

Yea the penalty on Z2 seems pretty severe, on top of that I will be using a low-power CPU on the N54L.

I am thinking with my limited capacity (maxed out at 5 disks here) Z1 is going to make the most sense.

 

[survive]

Hi par,

If you already have the disks you should try out raidz2 & see if it performs well enough before you dismiss it.

Raidz on 4TB disks is getting pretty...brave.

-Will

 

[par]

That is a good idea and I could do so, survive

Is anyone willing to break down the implications of usable storage vs parity in my case? It is difficult for me to interpret the wiki article on this decision.

 

[dcevansiii]

I second what survive said.

I would not use RAIDZ1. It is worth the $$ of the disk to use at least RAIDZ2 and maybe RAIDZ3.

Here are several good articles why:

1. http://www.zdnet.com/blog/storage/why-raid-5-stops-working-in-2009/162
2. http://www.zdnet.com/has-raid5-stopped-working-7000019939/

Oh and more importantly!

ALL of your disk will FAIL. ZFS will not help you if you do not KNOW that this has occurred.

So please, please setup regular scrubs and monitoring (email etc) so you will be there to replace a failing drive etc.

I was faced with a RAIDZ2 with 2 failed drives and all others degraded. I managed to get some new disks in there and all was good.
But until I did... ugh.

Don't do what I did.

 

[par]

I keep reading "don't use RAIDZ2 with 4k sector drives" when you have 5 disks.

Well, guess what I have :D

Still confused as to what the best option for me is here.
Z1 = big chance of loss
Z2 = not for 5 disks
Z3 = overkill

 

[cyberjock]

I keep reading "don't use RAIDZ2 with 4k sector drives" when you have 5 disks.

Well, guess what I have :D

Still confused as to what the best option for me is here.
Z1 = big chance of loss
Z2 = not for 5 disks
Z3 = overkill

I'd say that the real answer should be:

Z1 = big chance of loss
Z2 = good tradeoff between security and disk space
Z3 = overkill

Z2 isn't an "ideal" configuration, but for home use you aren't likely to care as your pool will be plenty fast anyway.

 

[par]

I'd say that the real answer should be:

Z1 = big chance of loss
Z2 = good tradeoff between security and disk space
Z3 = overkill

Z2 isn't an "ideal" configuration, but for home use you aren't likely to care as your pool will be plenty fast anyway.

Yea I just read about 10 articles and agree here and will be going with Z2.

There is a slight performance penalty due to having 5 4k disks but for my home usage it should pretty much be unnoticeable.

Thanks for the replies. In my case best to ignore optimal performance and bank on double parity.