LSI 9270-8i, inconsistent RAID5 performance with SAS Seagate 4 TB disks

Discussion in 'RAID Controllers and Host Bus Adapters' started by John B., Oct 23, 2018.

  1. John B.

    John B. New Member

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    Hello,

    I have recently acquired some second hand SAS Disks, Seagate 4 TB ST4000NM0023, I have 8 of them.
    To start with, I connected 4 of them to an LSI 9270-8i controller and created a RAID5 virtual drive.
    During my first tests, the read and write speeds were really good (400+ MB/s read and 350+ MB/s write).
    I then started copying several TB of data and after a couple of hours the write speed dropped severely and stayed around 95 MB/s.

    The difference I noticed is that, in the task manager, the virtual disk was first busy at round 85% and now that the speed has dropped down it is permanently at 100%.

    I am suspecting that one of the disk is slower than the other ones and is slowing down the whole array but I have quickly tested them one by one before creating the array and their individual speeds were in line with the specs (175 MB/s write).

    Any ideas?


    Thanks.

    John
     
    #1
  2. i386

    i386 Well-Known Member

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    "Up to 175mb/s" > that's when the disk is writing data to the outer tracks, inner tracks are slower.
     
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  3. John B.

    John B. New Member

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    Noted.
    I have a 4 other sata 3TB disks connected to the same controller, also in RAID5; the array is 75% full already but I am still getting write speeds around 250MB/s constantly so I am a bit puzzled.
     
    #3
  4. John B.

    John B. New Member

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    I am currently busy erasing the disks and I noticed that 2 disks are twice slower than the other 2...

    upload_2018-10-23_13-28-24.png
     
    #4
  5. schujj07

    schujj07 New Member

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    Possible that 2 of them are starting to fail and that would cause your performance to get worse. Also possible that first set of data was more sequential in type which would allow the drive to move faster vs more random data, or a bunch of smaller files, which would cause the drive to move slower.

    With 8 drives it would make more sense to run either a RAID 50 or RAID 60 for best performance.
     
    #5
  6. aero

    aero Active Member

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    Stripe, mirror, or parity.... Individual slow disks will slow down your array. I suggest throwing away the underperforming disks if you can consistently replicate their slow behavior in testing

    Edit: I'd also try moving the suspect disks to different ports as part of testing.
     
    #6
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