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Thread: VERY slow disk IO on OVH dedicated server..

  1. #1
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    Jul 2012
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    Default VERY slow disk IO on OVH dedicated server..

    Hi,

    Have setup ProxmoxVE on an OVH dedicated server using their install..

    The disk IO performance is VERY bad.. Has anyone else used their servers and worked out how to speed things up??

    Thanks.

    ~# pveperf /vz/
    CPU BOGOMIPS: 44685.28
    REGEX/SECOND: 1120717
    HD SIZE: 903.80 GB (/dev/mapper/pve-data)
    BUFFERED READS: 121.79 MB/sec
    AVERAGE SEEK TIME: 14.54 ms
    FSYNCS/SECOND: 17.81
    DNS EXT: 42.88 ms
    DNS INT: 3.01 ms (kimsufi.com)

  2. #2
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    Default Re: VERY slow disk IO on OVH dedicated server..

    What is the disk hardware ? do you use hardware raid ?

    (Kimsufi are the very low entry in ovh, so don't expect good performance)

  3. #3
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Thanks for the reply..

    We have two servers there now one is kimsufi and the other is OVH.. Both have shocking performance..

    No Hardware RAID on either but at less than 100 FSYNCS/Sec on both, the kimsufi one as above with less than 20 FSYNCS/Sec..

    Even my old Core2 desktop in my office that I use for testing things with old 500GB Seagate drives is able to get ~600 FSYNCS/Sec.. I don't understand why an old desktop can get more than 6 times the performance of a Xeon based server..

    There must be a reason because it just can't be THAT bad but I haven't had time to break it down to work it out yet.. Was hoping someone would have an idea..

  4. #4
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Do u have write cache and read cache enabled on disk?

  5. #5
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Quote Originally Posted by Kaya View Post
    Do u have write cache and read cache enabled on disk?
    Didn't change anything.. It's as it came..

    I have never changed anything on my test PC either, it just worked out of the box..

  6. #6
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Quote Originally Posted by wipeout_dude View Post
    Didn't change anything.. It's as it came..

    I have never changed anything on my test PC either, it just worked out of the box..
    What is the ouptut of
    hdparm /dev/sdX ?

  7. #7
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Quote Originally Posted by Kaya View Post
    What is the ouptut of
    hdparm /dev/sdX ?
    On the slower of the two servers..

    Code:
    root@in1:~# hdparm /dev/sd[abcd]
    
    /dev/sda:
     multcount     = 16 (on)
     IO_support    =  0 (default)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 121601/255/63, sectors = 1953525168, start = 0
    
    
    /dev/sdb:
     multcount     = 16 (on)
     IO_support    =256 (???)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 121601/255/63, sectors = 1953525168, start = 0
    
    
    /dev/sdc:
     multcount     = 16 (on)
     IO_support    =256 (???)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 121601/255/63, sectors = 1953525168, start = 0
    
    
    /dev/sdd:
     multcount     = 16 (on)
     IO_support    =256 (???)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 121601/255/63, sectors = 1953525168, start = 0
    On the Xeon server..

    Code:
    root@in2:~# hdparm /dev/sd[cd]
    
    /dev/sdc:
     multcount     =  0 (off)
     IO_support    =  1 (32-bit)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 243201/255/63, sectors = 3907029168, start = 0
    
    
    /dev/sdd:
     multcount     =  0 (off)
     IO_support    =257 (???)
     readonly      =  0 (off)
     readahead     = 256 (on)
     geometry      = 243201/255/63, sectors = 3907029168, start = 0

  8. #8
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Try a speed test on the slower one:

    hdparm -Tt /dev/sda

  9. #9
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Quote Originally Posted by Kaya View Post
    Try a speed test on the slower one:

    hdparm -Tt /dev/sda
    I have run those tests and get >100MB/s (Similar to pveperf result seen in the original post).. The issue doesn't appear to be raw throughput but IO/transactional performance which seems odd..

  10. #10
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Quote Originally Posted by wipeout_dude View Post
    I have run those tests and get >100MB/s (Similar to pveperf result seen in the original post).. The issue doesn't appear to be raw throughput but IO/transactional performance which seems odd..
    Yes, you only have 17.81 FSYNCS/SECOND. This indicates some kind of disks cache problem (maybe disk cache turned off?)
    Best regards,
    Dietmar

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  11. #11
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Probably a dumb question but how do you enable/disable the cache on SATA disks directly? (there is no hardware raid controller with and form of battery backed cache)

    Thanks..

  12. #12
    Join Date
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Check with:

    Code:
    proxmox-virt01:~# hdparm -W /dev/sda
    
    /dev/sda:
     write-caching =  1 (on)

  13. #13
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Appears to be on..

    Code:
     hdparm -W /dev/sd[abcd]
    
    /dev/sda:
     write-caching =  1 (on)
    
    
    /dev/sdb:
     write-caching =  1 (on)
    
    
    /dev/sdc:
     write-caching =  1 (on)
    
    
    /dev/sdd:
     write-caching =  1 (on)

  14. #14
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    Default Re: VERY slow disk IO on OVH dedicated server..

    what file system do you use, ext4? post the output of 'mount'
    Best regards,
    Tom

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  15. #15
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Was originally ext4.. Now setup with Btrfs and have attempted using Btrfs in a RAID10 configuration..
    Code:
    # btrfs filesystem df /var/lib/vzData, RAID10: total=10.00GB, used=8.10GB
    Data: total=8.00MB, used=0.00
    System, RAID10: total=16.00MB, used=4.00KB
    System: total=4.00MB, used=0.00
    Metadata, RAID10: total=2.00GB, used=40.86MB
    Metadata: total=8.00MB, used=0.00
    In the RAID10 configuration of btrfs the FSYNCS/Sec has improved but its still not near where it should be.. I would expect ~800-1000 FSYNCS/SEC in this configuration..

    Code:
    ~# pveperf /var/lib/vzCPU BOGOMIPS:      44689.36
    REGEX/SECOND:      1075265
    HD SIZE:           3596.77 GB (/dev/sda4)
    BUFFERED READS:    179.07 MB/sec
    AVERAGE SEEK TIME: 3.49 ms
    FSYNCS/SECOND:     120.46
    DNS EXT:           40.69 ms
    DNS INT:           45.41 ms (domain.com)
    I can only suspect a hardware issue but can't seem to figure out what it is especially when my years old desktop is able to nail the server in performance..
    Last edited by wipeout_dude; 08-25-2012 at 05:58 PM.

  16. #16
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    Default Re: VERY slow disk IO on OVH dedicated server..

    I can only suspect a hardware issue but can't seem to figure out what it is especially when my years old desktop is able to nail the server in performance.
    Did you install with ext3 on desktop?

  17. #17
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    Default Re: VERY slow disk IO on OVH dedicated server..

    btrfs? not really an option. if you donīt like ext3, maybe xfs can make you more happy.

    if your run openvz, ext3 is recommended.
    Best regards,
    Tom

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  18. #18
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    Default Re: VERY slow disk IO on OVH dedicated server..

    Is there an issue with ext4? Is that why you recommend ext3 or xfs?

    I know btrfs is still experimental and being copy-on-write will have a performance overhead but in a raid10 setup I thought the overhead would be mitigated.. Guess I was wrong..

  19. #19
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    Default Re: VERY slow disk IO on OVH dedicated server..

    ext3 is fast and stable, recommended for such boxes.
    Best regards,
    Tom

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