How to upgrade the raid

[dwf2008]

How are you arriving at 12 TB???
ZFS does not use "half the space" when using mirrors; it litterally "mirrors" (duplicate) the data over several drives. If you add the third drive to the existing vdev, you'll end up with a 3-way mirror vdev: Double redundancy, reasonably safe, but same 8 TB capacity.
If you were to add the third drive as a new (single drive) vdev, striped with the previous vdev, you'd end up with 16 TB of capacity but an unsafe setup: Failure of the single drive would take down the entire pool.

This is probably a stupid question, but could the third drive be split into two 4 tb partitions thereby appearing as 2 separate drives. Then using it as a second mirrored pool?

 

[Patrick M. Hausen]

What would be the capacity with that setup if the drives were 8 tb?

16 TB

 

[Patrick M. Hausen]

This is probably a stupid question, but could the third drive be split into two 4 tb partitions thereby appearing as 2 separate drives. Then using it as a second mirrored pool?

If that drive fails, then both parts of your "mirror" are gone and so is all the data. So what would be gained with such a setup?

 

[Etorix]

If you're desperate enough to ask that kind of question, it may be fair to conclude that ZFS is not for you and that you'd be happier—and safer!—with Unraid or OpenMediaVault.

 

[NugentS]

4 * 8TB, RaidZ2 = 16TB in round numbers. 8+8+((8+8) in parity)

 

[WI_Hedgehog]

4 * 8TB, RaidZ2 = 16TB in round numbers. 8+8+((8+8) in parity)

Or from a usability standpoint:

1 Boot drive + (3) 8TB Data drives
Data: 8TB
Mirror: 8TB (Mirror 1)
Mirror: 8TB (Mirror 2)
========
Data: 8TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 6.4TB (max), 6TB (realistic)

1 Boot drive + (4) 8TB Data drives
Data: 8TB
Data: 8TB
Parity: 8TB (RaidZ1)
Parity: 8TB (RaidZ2)
========
Data: 16TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 12.8TB (max), 12TB (realistic)

1 Boot drive + (5) 8TB Data drives
Data: 8TB
Data: 8TB
Data: 8TB
Parity: 8TB (RaidZ1)
Parity: 8TB (RaidZ2)
========
Data: 24TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 19.2TB (max), 18TB (realistic)

Every additional data drives adds 6TB of storage, up to 9 data-parity drives maximum per pool. Beyond 9 drives the pool starts to slow down, some pools have 12 drives though they are special cases.

 

[dwf2008]

If you're desperate enough to ask that kind of question, it may be fair to conclude that ZFS is not for you and that you'd be happier—and safer!—with Unraid or OpenMediaVault.

It was a theoretical question. Not something I would actually contemplate doing.

 

[dwf2008]

Or from a usability standpoint:

1 Boot drive + (3) 8TB Data drives
Data: 8TB
Mirror: 8TB (Mirror 1)
Mirror: 8TB (Mirror 2)
========
Data: 8TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 6.4TB (max), 6TB (realistic)

1 Boot drive + (4) 8TB Data drives
Data: 8TB
Data: 8TB
Parity: 8TB (RaidZ1)
Parity: 8TB (RaidZ2)
========
Data: 16TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 12.8TB (max), 12TB (realistic)

1 Boot drive + (5) 8TB Data drives
Data: 8TB
Data: 8TB
Data: 8TB
Parity: 8TB (RaidZ1)
Parity: 8TB (RaidZ2)
========
Data: 24TB
x 80% usable space (leaving 20% slack space for ZFS Copy-On-Write; 25% preferred)
========
Real-World Data: 19.2TB (max), 18TB (realistic)

Every additional data drives adds 6TB of storage, up to 9 data-parity drives maximum per pool. Beyond 9 drives the pool starts to slow down, some pools have 12 drives though they are special cases.

I failed to include that the boot drive is a separate 500 G drive. Sorry. So does that info get me to approx. 24 tb usable storage if only one is used for parity? Or are two parity drives required?

 

[Etorix]

Nothing is "required", but with large HDDs double parity is recommended.
Ultimately, it all depends on the level of resiliency you want to achieve, the quality of your backup strategy and how much you're willing to restore individual files and/or whole pool content from backup in the event of failure.

 

[dwf2008]

Nothing is "required", but with large HDDs double parity is recommended.
Ultimately, it all depends on the level of resiliency you want to achieve, the quality of your backup strategy and how much you're willing to restore individual files and/or whole pool content from backup in the event of failure.

Thank you Etorix.

 

[dwf2008]

If I understand correctly, and I have 4 x 8 tb drives for storage, I can set them up mirrored yielding 16 tb usable, or I can set them up as zfs raid2 also yielding 16 tb usable. So if the result is the same, is there one option that is better than the other?

 

[Patrick M. Hausen]

If I understand correctly, and I have 4 x 8 tb drives for storage, I can set them up mirrored yielding 16 tb usable, or I can set them up as zfs raid2 also yielding 16 tb usable. So if the result is the same, is there one option that is better than the other?

Mirrors give you more IOPS and faster resilver times, RAIDZ2 better fault tolerance.

 

[Etorix]

Correct.
Striped mirrors provide more IOPS, and would be the recommended layout for zvols or iSCSI. It is more flexible
Raidz2 is inflexible, but more resilient.

 

[dwf2008]

Are there any RAIDZ configurations where the capacity can be increased by adding more disks and without offloading the data and starting all over?

 

[ChrisRJ]

No. May I ask why you bring this up again? It has been covered multiple times already.

 

[dwf2008]

No. May I ask why you bring this up again? It has been covered multiple times already.

Sorry, just trying to bury old misunderstandings.
Thanks for your reply.

 

[WI_Hedgehog]

Are there any RAIDZ configurations where the capacity can be increased by adding more disks and without offloading the data and starting all over?

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