raid5 and 2 logical disk included in one zfs pool

[stamox]

Hello everyone,
What are your thoughts on adding two RAID5 logical disks into a single ZFS pool? How reliable would this setup be in terms of redundancy, and are there any specific considerations to keep in mind?

Thanks in advance.

 

[UdoB]

What are your thoughts on adding two RAID5 logical disks into a single ZFS pool?

Probably your terminology is wrong, there is no RAID5 in the context of ZFS. You probably mean RaidZ1 which represents a vdev (virtual device) with a single redundant device. One drive may fail without data loss.

Yes, you can have several of these in one pool.

You can lose one drive in each of these vdevs at the same time, without data loss.

ZFS is flexible: you can have a four drive RaidZ1 and a five disk RaidZ1 and a six drive RaidZ1 in the same pool. This is not recommended, but the ZFS semantics allows this.

There is a zillion options to construct a pool: if you want performance go for (multiple) mirrors only ... if you want high availability go for RaidZ3. The latter allows to get any three devices destroyed without data loss...

 

[stamox]

Probably your terminology is wrong, there is no RAID5 in the context of ZFS. You probably mean RaidZ1 which represents a vdev (virtual device) with a single redundant device. One drive may fail without data loss.

Yes, you can have several of these in one pool.

You can lose one drive in each of these vdevs at the same time, without data loss.

ZFS is flexible: you can have a four drive RaidZ1 and a five disk RaidZ1 and a six drive RaidZ1 in the same pool. This is not recommended, but the ZFS semantics allows this.

There is a zillion options to construct a pool: if you want performance go for (multiple) mirrors only ... if you want high availability go for RaidZ3. The latter allows to get any three devices destroyed without data loss...

"Probably your terminology is wrong, there is no RAID5 in the context of ZFS. You probably mean RaidZ1 which represents a vdev (virtual device) with a single redundant device. One drive may fail without data loss."
Allow me to disagree with you. I’m talking about a RAID 5 made by a hardware controller, then add a logical disks in to the pool. Topic of the post : raid5 and 2 logical disk included in one zfs pool

Best regards, and thank you for your time.

 

[Onslow]

I’m talking about a RAID 5 made by a hardware controller, then add a logical disks in to the pool.

Well,
"Do not use ZFS on top of a hardware RAID controller which has its own cache management. ZFS needs to communicate directly with the disks. An HBA adapter or something like an LSI controller flashed in “IT” mode is more appropriate."

( https://pve.proxmox.com/wiki/ZFS_on_Linux ).

Technically it's probably possible, but as you have asked "What are your thoughts", then I'm answering:
it's not a good idea .

 

[stamox]

Thank you for your opinion.

 

[UdoB]

I’m talking about a RAID 5 made by a hardware controller

Okay, so my understanding was wrong, sorry.

I'm with @Onslow in#4. ZFS should have direct access to each physical device. With a hardware Raid controller that's not the case...

A lot of controllers have an "HBA"-mode selectable in their Bios or can be flashed to switch to the mentioned "Initiator-Target"-mode. Check if that's possible for your controller.

 

[stamox]

Hello,

Many thanks for ALL.