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Thread: mdadm RAID0 very slow read speeds

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    Join Date
    Mar 2009

    mdadm RAID0 very slow read speeds

    Hi, I'm switching over from FreeNAS to Ubuntu Server 12.04 for my NAS box and am converting my ZFS pools to mdadm RAIDs and am having some serious issues reading/streaming files over SMB.

    Server is AMD E-350 APU with 8GB DDR3 RAM.

    I have two 1.5TB hard drives of different makes in a RAID0 configuration, and then shared over the network using samba.

    Individually, one drive would copy over SMB to my desktop at 100 MB/s, the other at around 70 MB/s. (the first is a Seagate ST1500DL003 5900 RPM drive and the second is a WD Green WD15EADS with a few more hours under its belt.)

    When striped together, I get a MAX of 10 MB/s under the same network conditions. When ssh'd into the server browsing the drive simply doesn't feel snappy either. Totally different than my old ZFS stripe which worked fine.

    Here's what I used to create the RAID and create the file system:

    parted -a optimal /dev/sdb
        mkpart primary 1MiB 100%
        set 1 raid on
    parted -a optimal /dev/sdc
        mkpart primary 1MiB 100%
        set 1 raid on
    mdadm --create --verbose /dev/md0 --level=stripe --chunk=32 --raid-devices=2 /dev/sdb1 /dev/sdb2
    mkfs.ext4 -b 4096 -E stride=8,stripe-width=16 /dev/md0
    tune2fs -O has_journal -o journal_data_writeback /dev/md0
    tune2fs -O dir_index /dev/md0
    e2fsck -D /dev/md0
    mdadm --detail --scan >> /etc/mdadm/mdadm.conf
    mount /dev/md0 /mnt/storage -o noatime,nodiratime,data=writeback,stripe=16,barrier=0,errors=remount-ro
    I understand some of my file system options may be risky, but I tried it yesterday with the defaults (didn't specify chunk, stride, stripe-width; no journal tuning) and got the same result.

    I also know that I will lose the stripe if I lose one drive, I understand that, I have nightly backups running.

    Here's some more information:

    #cat /proc/mdstat
    Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
    md0 : active raid0 sdb1[0] sdc1[1]
          2930274240 blocks super 1.2 32k chunks
    unused devices: <none>
    #mdadm -D /dev/md0
            Version : 1.2
      Creation Time : Sat Aug 10 16:20:23 2013
         Raid Level : raid0
         Array Size : 2930274240 (2794.53 GiB 3000.60 GB)
       Raid Devices : 2
      Total Devices : 2
        Persistence : Superblock is persistent
        Update Time : Sat Aug 10 16:20:23 2013
              State : clean 
     Active Devices : 2
    Working Devices : 2
     Failed Devices : 0
      Spare Devices : 0
         Chunk Size : 32K
               Name : oldtown:0  (local to host oldtown)
               UUID : e50ae570:427d0db7:475bc4cc:8f86f703
             Events : 0
        Number   Major   Minor   RaidDevice State
           0       8       17        0      active sync   /dev/sdb1
           1       8       33        1      active sync   /dev/sdc1
    #hdparm -tT /dev/md0
     Timing cached reads:   2122 MB in  2.00 seconds = 1060.41 MB/sec
     Timing buffered disk reads: 302 MB in  4.59 seconds =  65.80 MB/sec
    #dd if=/dev/zero of=testfile bs=1M count=5000
    5000+0 records in
    5000+0 records out
    5242880000 bytes (5.2 GB) copied, 65.2134 s, 80.4 MB/s
    #dd if=testfile of=/dev/zero bs=1M
    5+0 records in
    5+0 records out
    5242880000 bytes (5.2 GB) copied, 4.0535 s, 1.3 GB/s
    #dd if=/dev/zero of=testfile bs=1000M count=5
    5+0 records in
    5+0 records out
    5242880000 bytes (5.2 GB) copied, 65.4636 s, 80.1 MB/s
    #dd if=testfile of=/dev/zero bs=1000M
    5+0 records in
    5+0 records out
    5242880000 bytes (5.2 GB) copied, 5.69963 s, 920 MB/s
    #time cp testfile testfile2
    real 2m42.178s
    user 0m0.100s
    sys 0m19.525
    Excerpt from smb.conf
    guest ok=yes
    create mask=0744
    directory mask=0755
    read only=no
    follow symlinks=yes
    wide links=no

    Thanks in advance for your help!

    Also for what it's worth, the 3TB drive is running UFS right now and when samba shared transfers at a speedy 100 MB/s.
    Last edited by hansamurai; August 11th, 2013 at 01:13 AM.


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