This discussion is archived
9 Replies Latest reply: Apr 16, 2013 1:12 AM by tbrinkmann RSS

Disk IO issues on OVM System

tbrinkmann Explorer
Currently Being Moderated
Hi all,
we face a problem regarding disk IO on local build disk array. We use a HPG7 server with an raid51 array.

We use two of these machines for an oracle rac. The problem occurs on both systems.

We run a ovs-release-2.2-2.0
kernel: 2.6.18-128.2.1.4.44.el5xen

So i try to check the disk speed by creating a test file with dd.

#>dd if=/dev/zero of=test.file bs=8K count=80000
--> (655 MB) copied, 11.7443 seconds, 55.8 MB/s

While the data was copied I also checked the disk IO with iostat and can see that the c0d0p3 disk array
speed is around 55/MB7s

--> cciss/c0d0 608.91 0.00 55.95 0 56

So my question: Does anyone could help me digging this out ? I do not really know where to start.
Some kernel parameter ? Hardware ? Diskarray ?

Thanks a lot !
*T                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
  • 1. Re: Disk IO issues on OVM System
    Dude! Guru
    Currently Being Moderated
    You did not describe your problem, but I assume it's about the disk throughput performance results. You might be able to improve performance by using paravirtualized (PV) drivers for network and block devices on Oracle Linux guests running in a virtual Oracle VM environment.

    The following should give you some ideas: http://docs.oracle.com/cd/E26996_01/E18549/html/BABICHHG.html

    If you need more help, it might be better to request help from Oracle support or to continue your post in the Oracle VM forum.
  • 2. Re: Disk IO issues on OVM System
    alvaromiranda Explorer
    Currently Being Moderated
    on topof what dude have suggested,

    1. if the guest are Oracle Linux, you can use in OL6 and OL5 UEK2 Kernel.

    2. Are you using asmlib for the ASM disks?

    3. For the filesystem holding oracle_home, are you using ext4? if you are on ext3, I have seen sometimes that the system behave poorly.
    You can convert to ext4, and that will improve the performance.

    Alvaro.
  • 3. Re: Disk IO issues on OVM System
    tbrinkmann Explorer
    Currently Being Moderated
    Hi,
    the problem occurs directly on the OVM(dom0) and of course also on the OVM Guests.

    All our guest systems are running as PV with OL5.8 and UEK 300
    2.6.32-300.38.1.el5uek
    There are only three VM Guests are running.

    The oracle homes are located on ext4.

    May I need to create an SR :-/ But I also will try to find more information.

    Thanks a lot !
  • 4. Re: Disk IO issues on OVM System
    tbrinkmann Explorer
    Currently Being Moderated
    Re,
    the problem is regarded to the direct write to disk. With no cashing the write speed ist slower than 1MB/s

    :/
  • 5. Re: Disk IO issues on OVM System
    Dude! Guru
    Currently Being Moderated
    With no cashing the write speed ist slower than 1MB/s
    No cash no fun! (ohne Moos nix los) ;-) Perhaps you have an issue with HVM and PVM. The problem could however also be your hardware and not the operating system or Oracle VM.

    Anyway, to discuss your options, it might be better to use the Oracle VM forum for closer topic alignment.
  • 6. Re: Disk IO issues on OVM System
    rukbat Guru Moderator
    Currently Being Moderated
    tbrinkmann wrote:
    the problem occurs directly on the OVM
    +... thread moved from the Oracle Linux forum to the OVM forum ...+
  • 7. Re: Disk IO issues on OVM System
    alvaromiranda Explorer
    Currently Being Moderated
    on the OVM Server do
    hdparm -tT /dev/<disk>

    That will tell you the read speed for cache and disk

    Do the same fot disk and partition on couple of disks, then repeat on 1 Host.

    That will show if the speed is consistent or no.


    if you want to do similar for writing, use

    dd oflag=direct if=/dev/disk of=/path/to/file bs=1M count=1000

    That will write a file of 1GB

    Also, paste one vm.cfg file of one of the guest to have a look.
  • 8. Re: Disk IO issues on OVM System
    Avi Miller Guru
    Currently Being Moderated
    tbrinkmann wrote:
    We run a ovs-release-2.2-2.0
    Oracle VM 2.2.2 has a 32-bit Dom0 running the old 2.6.18 kernel, which is ancient. You really should look at upgrading to Oracle VM 3.2.1 which uses the UEK2 64-bit Dom0 kernel and will probably be a lot faster on this hardware. Also, 64-bit guests should usually be run in HVM with PV Drivers mode for optimum performance.
  • 9. Re: Disk IO issues on OVM System
    tbrinkmann Explorer
    Currently Being Moderated
    We will update to 3.2.1 and give it a try

Legend

  • Correct Answers - 10 points
  • Helpful Answers - 5 points