RaidZ2 with 5 drives non-optimal warning

[skimon]

Hello,

While i was briefly in the zfs volume manager freenas 9.2.1.9 last night and i added all 5 disks to a zpool it gave me a warning when switching from RaidZ1 to RaidZ2 . Specifically it gave a warning that 5 disks (3TB WD Reds) in RaidZ2 is not optimal and pointed me to a chapter in the manual for more details. I looked through that section again but i couldnt find anything specific to this setup.

Does anyone know what exactly it is warning about , and whether I should really heed that warning and take RaidZ1 instead or rethink my setup ?

Thanks

 

[Apollo]

If you are starting a new build or adding another zvol to your system, you might want to consider upgrading to Freenas 9.3. It has some nice features 9.2 doesn't have.
Theorectically, there is no issues as pointed out by the announcement of "A Complete Guide to FreeNAS DesignPart III: Pools, Performance and cache" on the freenas.org main page.
However, I did experiment with higher than 6 and I had to use manual setup to accomplish it. I wasn't too happy with the results as it seems one of the drive was not getting any throughput. Could have been the drive (I did experiment will old drives past there primes anyway). You may have better luck with 9.3 though.
If you could add one more drive to reach the count of 6, then you will have no issues at all.

Other than performance hit, I don't think it matters. The warning may be deprecated and may possibly be irrelevant.

 

[skimon]

If you are starting a new build or adding another zvol to your system, you might want to consider upgrading to Freenas 9.3. It has some nice features 9.2 doesn't have.
Theorectically, there is no issues as pointed out by the announcement of "A Complete Guide to FreeNAS DesignPart III: Pools, Performance and cache" on the freenas.org main page.
However, I did experiment with higher than 6 and I had to use manual setup to accomplish it. I wasn't too happy with the results as it seems one of the drive was not getting any throughput. Could have been the drive (I did experiment will old drives past there primes anyway). You may have better luck with 9.3 though.
If you could add one more drive to reach the count of 6, then you will have no issues at all.

Other than performance hit, I don't think it matters. The warning may be deprecated and may possibly be irrelevant.

Thanks for your reply. Is there anything in 9.3 that i cant get if i creste the zvols in 9.2 and then upgrade the firmware? I ask because i had troubles with plugins on 9.3 in my virtual (Sandbox only) so im reluctant to use it unless it some killer features thst i cant get later without recreating my pool.

 

[Apollo]

Thanks for your reply. Is there anything in 9.3 that i cant get if i creste the zvols in 9.2 and then upgrade the firmware? I ask because i had troubles with plugins on 9.3 in my virtual (Sandbox only) so im reluctant to use it unless it some killer features thst i cant get later without recreating my pool.

Under 9.3 you can use a zvol created under 9.2. Just don't upgrade the volume until you are sure you will never go back to 9.2 otherwise releases prior to 9.3 will not be able to access the pool.

 

[Bidule0hm]

The warning is just about a performance issue, but generally the network is the bottleneck and even with a non-optimal number of disks per vdev you can easily saturate a gigabit link. Moreover when compression is enabled (and it is enabled by default in the 9.3 version and even in the 9.2 IIRC) it reduces almost completely the impact of this problem, see this article for more info http://blog.delphix.com/matt/2014/06/06/zfs-stripe-width/ ;)