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Thread: Slow Raid Performance

  1. #1
    Join Date
    May 2013
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    6

    Slow Raid Performance

    Hi every one,

    I have built a little NAS server and the performance is not as expected.

    The components i have used are AsRock A75 motherboard, AMD A4 APU, 4Gb 1600MHz RAM, 4 Drive Back Plain, Intel Gigabyte Network Card and 4x 3TB Seagate Barracuda Hard Drives

    I frist created the RAID using mdadm in RAID level 5, after doing some testing over the network and on the host I was only abel to achieve around 100MB per second read / wright.
    That lead me to the conclusion that maybe RAID 5 was probably to much for the system.

    So after backing up my data I deleted my RAID volume and set out to initialise raid 10.

    After all the hard drives where ready I repeated the same tests, the read wright speed did increases form 100MB to 110MB per second.

    I was expecting faster read speeds, I have tested all the drives individually all averaging 150MB/s +-10MB

    is their some form of bottleneck in my configuration or some software issue preventing me form getting faster speeds?

    Or will I have to buy a RAID card to get better performance?

    Thanks,

  2. #2
    Join Date
    Sep 2008
    Location
    Netherlands
    Beans
    369
    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: Slow Raid Performance

    100MB/s is close to the max on a Gigabit network. 125MB/s is hard to achieve because of overhead.


    Internal speeds can be increased with disk/raid parameter tuning.

    /sys/block/md0/md/stripe_cache_size
    blockdev --getra /dev/md0

    These are two I found important for my raid5 setup.
    Chunk size helped me also for raid5. I use a massive 2048k.

  3. #3
    Join Date
    May 2013
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    6

    Re: Slow Raid Performance

    This might sound completely stupid but .... really the overhead in a gigabyte network is that much???

    I should of gotten a Thunderbolt connection.

    can you play with the strip size in a live raid setup?

  4. #4
    Join Date
    Nov 2008
    Location
    Sheffield, UK
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    Ubuntu

    Re: Slow Raid Performance

    on local machine what's output of

    sudo hdparm -Tt /dev/md0

  5. #5
    Join Date
    May 2013
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    6

    Re: Slow Raid Performance

    Quote Originally Posted by SlugSlug View Post
    on local machine what's output of

    sudo hdparm -Tt /dev/md0
    Code:
     /dev/md0
        Timing cached reads: 4176 MB in 2 seconds = 2087.99 MB/sec
             Timing buffered disk reads: 908 MB in 3.00 seconds = 302.46 MB/sec

  6. #6
    Join Date
    Nov 2008
    Location
    Sheffield, UK
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    1,517
    Distro
    Ubuntu

    Re: Slow Raid Performance

    on my 4 disk raid0 I get about 400MB/s using hdparm.

    Looks like your issue is network speeds

  7. #7
    Join Date
    May 2013
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    6

    Re: Slow Raid Performance

    I thought that as well till I coped one file to and other folder on the local host and it was getting the same speed.
    when I was running raid 5 I could hit 900MBS but then it would drop to around 90.


    RAID 0 some one likes to live Dangerous

  8. #8
    Join Date
    Nov 2008
    Location
    Sheffield, UK
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    Ubuntu

    Re: Slow Raid Performance

    Its basically just a download drive sees plenty of unrar'ing not to bothered if I lose whats on it

    That might be the hardware limits your hitting was the file/folder you copied / pasted to on same raid or different drives? If teh drives have to read and write at the same time that'll slow you down

    you could try

    write speed:
    dd if=/dev/zero of=/mnt/raid0/output bs=100k count=20k;
    20480+0 records in
    20480+0 records out
    2097152000 bytes (2.1 GB) copied, 5.27545 s, 398 MB/s



    read speed:
    dd if=/mnt/raid0/output of=/dev/null bs=100k
    20480+0 records in
    20480+0 records out
    2097152000 bytes (2.1 GB) copied, 3.04066 s, 690 MB/s

  9. #9
    Join Date
    May 2013
    Beans
    6

    Re: Slow Raid Performance

    I'm playing with saturnusDJ's advice. But going back to raid5 looks good at the moment but going to have to wait for the drives to compleat setup before I can see some real numbers but got 300MBs in one test

  10. #10
    Join Date
    Sep 2008
    Location
    Netherlands
    Beans
    369
    Distro
    Ubuntu 12.04 Precise Pangolin

    Re: Slow Raid Performance

    Yes the parameters may be changed live! Chunk size can not be changed after creating an array.

    For testing you can create an array existing of small partitions. Then the resync won't take long. Only keep in mind hard drives drop speed near the end.

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