Mixing 7200 rpm drive and green one in mirror vdev

[Delivereath]

Hi,

I've a mirror vdev with one disk having some SMART test errors. The mirror is built with 2x 2 TB WD green drives. I would like to replace the bad disk with a 4 TB Hitachi Deskstar (7200 rpm) disk.

Is there any risk doing that ? I know that access time and read/write speeds will not get close to what I could have with a 2x 7200 rpm mirror but I have no need for high speed. As long as my disks are not being stressed too much because of this setup, I'm good with it.

What about head parking on Hitachi drivers ? I've increased the head parking delay on my green drivers. Can this be done on Hitachi drivers too ?

Finally, one point regarding vdev mirrors. Based on this article, http://jrs-s.net/2015/02/06/zfs-you-should-use-mirror-vdevs-not-raidz/, I'm planning to move my RaidZ1 to mirrors. At the moment, I've 8 disks. I'm wondering if it's better to have multiple zpools, each one being a single mirror vdev with 2 disks, or if I should go to a single zpool with 4 mirror vdevs. The single zpool solution will have higher performance but also a higher risk because losing a single vdev (2 dead disks on the same mirror vdev) would kill the complete zpool.

What is your opinion regarding this ?

Thanks !

 

[Bidule0hm]

I don't see any problem, you can do that ;)

What about head parking on Hitachi drivers ?

I don't know but I guess you'll have an answer if you search on the web.

At the moment, I've 8 disks. I'm wondering if it's better to have multiple zpools, each one being a single mirror vdev with 2 disks, or if I should go to a single zpool with 4 mirror vdevs. The single zpool solution will have higher performance but also a higher risk because losing a single vdev (2 dead disks on the same mirror vdev) would kill the complete zpool.

It depends, in the end it's up to you to chose between the two options :)

NB: a mirror is safer than a RAID-Z1 (even a 3 drives one) for same size drives.

 

[BigDave]

I've a mirror vdev with one disk having some SMART test errors. The mirror is built with 2x 2 TB WD green drives. I would like to replace the bad disk with a 4 TB Hitachi Deskstar (7200 rpm) disk.

Is there any risk doing that ?

The ZFS Primer mentions no warning other than the replacement disk (4TB Hitachi) would be resilvered into your pool at
2TB in size (matching the existing green drives).
Creating vdevs using the same size disks is recommended best practice.