Which drive setup is the less "wrong"...

[x-cimo]

What would be the most optimal setup for

6x 2TB drives (already have thoses)
2x or 3x 4TB drives (will be buying them)

Should I favor same size VDEV by mixing vdev type (mirror/raidz/raidz2):
4TB: raidz (3x2TB )
4TB: raidz (3x2TB )
4TB: Mirror (2x4TB )

or should I favor same type VDEV, and have an unbalanced Pool?
2TB: Mirror( 2x2TB )
2TB: Mirror( 2x2TB )
2TB: Mirror( 2x2TB )
4TB: Mirror( 2x4TB )

or even play with number of drive within a vdev:

8TB: raidz2 ( 6x2TB )
8TB: raidz1 ( 3x4TB )

This is kinda a tricky one, worst case I can always create two pool but I would loose in striping over vdev performance.

Thanks you.

 

[fracai]

The primary point that jumps out for me is to keep in mind that if you loose a VDEV, it takes down your whole pool. So that would rule out the last option. Also, I think you'll be limited by the speed of the slowest VDEV, which would rule out the first option. I think the "all mirrors" option looks the best, or add another 4TB and go with the last option, but both being Z2.

Also remember that you can't expand a VDEV by adding disks. You can replace disks with larger capacity to expand the VDEV capacity, but you can't turn a 6 drive Z2 into an 8 drive Z2. Consider that when deciding how to group your disks.

 

[x-cimo]

The primary point that jumps out for me is to keep in mind that if you loose a VDEV, it takes down your whole pool. So that would rule out the last option. Also, I think you'll be limited by the speed of the slowest VDEV, which would rule out the first option. I think the "all mirrors" option looks the best, or add another 4TB and go with the last option, but both being Z2.

Also remember that you can't expand a VDEV by adding disks. You can replace disks with larger capacity to expand the VDEV capacity, but you can't turn a 6 drive Z2 into an 8 drive Z2. Consider that when deciding how to group your disks.

Thanks for your reply,

In order to prevent unexpected performance issue due to mixed disk size, different sector size and mixed vdev type, I am pretty much set on creating a second Pool with only 4TB drives.

I think it will pay in the long run, as I add more disk to it and also split my the data into two managable sized Pool if I want to break either onea apart.

Hopefully its gonna help someone in a similar situation.

I wish I had 3 free 2TB 512B sector size (in raidz) that I could have tested with 2 4TB 4K Sector size (in mirror), that I could have tested if there was really an issue with doing that.. Maybe next time.

 

[paleoN]

In order to prevent unexpected performance issue due to mixed disk size, different sector size and mixed vdev type, I am pretty much set on creating a second Pool with only 4TB drives.

FYI, I wouldn't consider running 4TB drives in anything less than double-parity arrays.

I think it will pay in the long run, as I add more disk to it and also split my the data into two managable sized Pool if I want to break either onea apart.

Not quite sure what you mean, but you can't remove vdevs from a pool once they are added.

I wish I had 3 free 2TB 512B sector size (in raidz) that I could have tested with 2 4TB 4K Sector size (in mirror), that I could have tested if there was really an issue with doing that..

Keep in mind ashift is set, and can't be changed, during vdev creation. In other words force 4k if you are going to replace the drives with 4k native ones later. Otherwise, migrate.

 

[x-cimo]

FYI, I wouldn't consider running 4TB drives in anything less than double-parity arrays.

Not quite sure what you mean, but you can't remove vdevs from a pool once they are added.

Keep in mind ashift is set, and can't be changed, during vdev creation. In other words force 4k if you are going to replace the drives with 4k native ones later. Otherwise, migrate.

PaleoN, do you include mirror in "double parity array"? I was to create my new Pool as an array of 4TB mirrors.

I said it would pay in the long run to place the 4TB in a new array, because I can't do proper testing right now since my 2TB drives are in use, I can't break that array at that point, so if the mix didin't cut it, i would be stuck with an array so big that I couldn't move it's data.

The second pool let me think about it, and provided a second pool to copy data to, therefore the next time I need to add drives I should be good to test with the new drives and the 2TB, while leaving the data on this first set of 4TB drives.

It's also kinda nice to be able to move data between two pool if I want to make change to either ones, but will loose a bit in performance from having everything in the same pool.

Thanks!

 

[fracai]

I think the 4TB / double parity concern is that if one of your drives dies, even if you immediately replace it, the re-silver is going to put a lot of stress on the good drive. The higher the ratio of disk size to parity is equivalent to a higher risk of another good drive dying before the re-silver completes. So in that sense, a mirror is definitely not double parity.

 

[paleoN]

PaleoN, do you include mirror in "double parity array"?

Three-way mirror. Though at low spindle counts raidz2 arrays seem to make much more sense.

It's also kinda nice to be able to move data between two pool if I want to make change to either ones, but will loose a bit in performance from having everything in the same pool.

A second pool can give you a number of options. The main thing is to plan out how you are getting to your fully built configuration.