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12 hdds - 100MB/s streaming reads and writes and 250 read and write IOPS. When i do 2xRAIDZ2 so there is 2 vdev 6 HDD each the theoretical IOPS will be 500 according to this atricle: https://www.ixsystems.com/blog/zfs-pool-performance-2/?unapproved=2604&moderation-hash=32113df8ab58c6c0bf4badb998b919e8#comment-2604 The question is if i will do 3xRAIDz2 ( 3vdevs 4HDD each ) will IOPS increase to 750 ?

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This is easy enough to test on your own... but the values you have are super low.

For me, 2 x RAIDZ1 and 2 x RAIDZ2 are the fastest for sequential (streaming) workloads on 7200 RPM drives. I see 1.3 Gigabytes/second read and 1.1 Gigabytes/second write in this setup.

IOPS are going to be a function of block size and access pattern, so that's difficult to predict unless you provide more workload details.

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  • The numbers are theoretical - i just want to know if this change will increase iops or not .
    – Kriss
    Jul 4, 2019 at 9:38
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Yes, just like striping across disks with regular RAID0, when striping zfs datasets across same-config VDEVs, IOPS will scale with the number of IOPS each VDEV can service. For RAIDZ2, typical IOPS is that of a single spindle, or 250 IOPS in your case. 2x RAIDZ2 striped = ~500 IOPS and 3x RAIDZ2 striped = ~750 IOPS.

While the 3x RAIDZ2 stripped config is not explicitly presented, the actual benchmarks with varying zpool configurations available at this link clearly show a linear progression for stripping across VDEVs. You may also find these various benchmarks useful reference while planning your zpool layouts: https://calomel.org/zfs_raid_speed_capacity.html

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