Optimum number of drives

[hellokevin11]

Is it true that for ZFS raid, it's best to have a number of drives evenly divisible plus the parity drives?

Windows would be :6,8,10,12 and parity is across all the drives

ZFS is 6,8,10,12 etc + number of parity drives.

So to get 12TB, I would run 12 drives plus 3 parity drives. 15 drives?

I am quoting from a web site:

"RAIDZ-3 (raid7) with three parity you should use five (2+3), seven (4+3), eleven (8+3), or nineteen (16+3) disks."

So I am confused on this. The maximum number of drives I can install is 14 drives. I currently have 12.

Should I add another disc so it is 10+3 ?

[crowi]

It depends on what you aim. Do you really need RAIDZ3 or would Z2 also be sufficient?
Actually you CAN do a RAIDZ3 with 12 disks, you just won't get the maximum possible IOPS.
With Z3 the performance will be lower than Z2 or Z1
https://forums.freebsd.org/viewtopic.php?t=43981
But you can overcome this to a certain extent, if you provide enough memory and possibly by using SSDs as log and cache devices.
http://constantin.glez.de/blog/2010/06/ ... erformance

[raulfg3]

more and acurrate info here: viewtopic.php?f=66&t=6829#p38844

[hellokevin11]

It depends on what you aim. Do you really need RAIDZ3 or would Z2 also be sufficient?
Actually you CAN do a RAIDZ3 with 12 disks, you just won't get the maximum possible IOPS.
With Z3 the performance will be lower than Z2 or Z1
https://forums.freebsd.org/viewtopic.php?t=43981
But you can overcome this to a certain extent, if you provide enough memory and possibly by using SSDs as log and cache devices.
http://constantin.glez.de/blog/2010/06/ ... erformance

I'm not too knowledgeable about arc and l2arc, are they stable in the current nas4free?
Many of the posts I am reading mention corruption issues.

I need ZFS-Z3 because most of the drives were my leftovers or free from other projects.
While 50% are new, 25% are at least 3 years old NEW old stock spares that were EOL.
The other 25% are old drives that were used. I did a full extended test on all, and plan to do a 30 day
burn in.

I've just read some posts about if your number of drives and / or alignment is off that a lot of space can be lost due to partially filled sectors on incorrectly aligned drives.

This is my first foray into BSD and linux, so all I know is wintel. You'll have to exercise a bit of patience with my questions, thanks.

I'll be burying myself in the faqs for a few days it looks like.

[crowi]

I'm not too knowledgeable about arc and l2arc, are they stable in the current nas4free?

arc is placed in RAM, L2ARC is usually placed on SSDs
And yes, it is stable


You might get alignment an thus performance issues if you mix 4k drives and 512b sector drives in one vdev.
Here it would be better to create two vdevs with the drives of matching sector size.
The two vdevs can then be combined in one pool.

[hellokevin11]

Ok so now I have 13 drives 10+3 parity, and SSD for l2arc

Memory will be here soon, and then I will do burn in on the system.

The older drives are not 4K capable, so I will have to do smaller "standard" sectors.

[crowi]

The older drives are not 4K capable, so I will have to do smaller "standard" sectors.

Not a good idea, you will get bad performance when running 4k drives on 512 format.
It would be really better to combine all 4k drives in one vdev and all non-4k-drives in another vdev

[b0ssman]

if you alight 512 drives using the 4k alignment there is no performance hit. (you just loose a few sectors of space)

if you align 4k drives using the 512 alignment there is a performance hit.

[hellokevin11]

if you alight 512 drives using the 4k alignment there is no performance hit. (you just loose a few sectors of space)

if you align 4k drives using the 512 alignment there is a performance hit.

Ok thanks again for the information.