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  • UNRAID ZFS HYBRID MODE READ SLOW READ MULTIPE DISK

    competent-bailout3425

    By competent-bailout3425

      • Minor

    I have 9 disks for zfs format data disk and 2 parity disk for unraid array.When I read data from 9 data disks simultaneously through /mnt/diskx, the overall throughput is very low, only 300M/s, slightly higher than the throughput of a single disk (260M/s). At the same time, I can see that my 32-core 7d12 CPU is almost fully loaded in the background. By using the "top" command, I can see that processes like unraidd1 and unraidd2 are consuming a significant amount of CPU.

    I have confirmed that my hard disk bandwidth is sufficient to support all my disks being fully loaded for reading simultaneously. During parity check, all 11 hard disks can operate at speeds above 250M/s.

     

    some test:

    3disks

    image.thumb.png.4c4c4a27a1bb15b2461a194161ca5cba.png

    image.thumb.png.fcd064e658f5edd3c0dd5941540264fa.png

    9disks

    image.thumb.png.8a5e94bb1e727b4de3d87397e65c38b3.png

    image.thumb.png.b09ee5a4204469949b314ceae7adec83.png

     

    It is highly likely that Unraid has assigned a separate kernel thread for each disk to handle IO requests,but miuse spin locks during those thread(more disk,slow thorughput,but higher cpu usage).

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    JorgeB

    I can also reproduce the issue, reading the same zfs formatted three devices simultaneously in the array vs using separate pools:

     

    zfs.JPG

    450MB/s total

     

    image.png

    785MB/s total

     

     

     

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    competent-bailout3425

    It seems that no one is addressing this issue? This problem also occurs during filesystem checks. When I try to check the filesystems on multiple hard drives, I encounter the same issue. I can only check up to three hard drives at a time, otherwise, the total throughput will decrease. This situation has a significant impact, and I hope it can be resolved as soon as possible.

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    JorgeB

    It's been reported, possibly not considered a high priority issue, but it should be fixed in the near future.

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