vSphere Storage Appliance

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  • 1.  Large IO block size (writes / read), High latency..

    Posted May 16, 2012 08:29 AM

    Hello,

    I have an issue with my storage (EQL PS6100 24x 600GB 15k sas in raid 50). When i do a simple file copy within a VM its very slow, after investigation i discoverd that vmware and my san reports a very high write / read latency when i generate bigger (64kb +) io blocks. Besides that, when i go above 128KB blocksize my san keeps reporting its doing 128KB blocks. Even when i generate 256 or 512KB blocks. I installed windows directly on the same hw and ran the same tests then i have no problem what so ever (also the high latency is allmost gone)..

    I`m testing with iometer:

    512b 100% write 0%random

    4kb 100% write 0%random

    16kb 100% write 0%random

    32kb 100% write 0%random

    64kb 100% write 0%random

    128kb 100% write 0%random

    256kb 100% write 0%random

    512b 100% read 0%random

    4kb 100% read 0%random

    16kb 100% read 0%random

    32kb 100% read 0%random

    64kb 100% read 0%random

    128kb 100% read 0%random

    256kb 100% read 0%random

    physical:

    virtual:

    Everything is latest version, mem driver, eql firmware, nic drivers, esx etc etc

    I`m using dell switches (pc62xx) and a mix of r610+r620+PE1950/2950

    Regards



  • 2.  RE: Large IO block size (writes / read), High latency..

    Posted May 16, 2012 02:39 PM

    Hello.

    Note: This discussion was moved from the VMware ESXi 5 community to the VMware vSphere™ Storage community.

    Good Luck!



  • 3.  RE: Large IO block size (writes / read), High latency..

    Posted May 16, 2012 05:55 PM

    You can try to set the parameter "Disk.DiskMaxIOSize" to 64. This will limit the IO-Size to 64 KB and larger IO-request will be splitted.

    You can change the parameter without rebooting the ESX host.

    Some arrays perform better with this setting. I would also use the "Paravirtual SCSI-Controller" within the VM for maximum performance.

    Look at this KB for the parameter setting:

    http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003469



  • 4.  RE: Large IO block size (writes / read), High latency..

    Posted May 16, 2012 07:44 PM

    thanks, but what i mean: its like the io is already splitted by vmware? Cause i generate a 256KB but that gets splitted back to 128kb...



  • 5.  RE: Large IO block size (writes / read), High latency..

    Posted May 19, 2012 12:36 PM

    just heared from vmware that 128 is the default size, they will "split" any block that is larger then that back to 128KB...



  • 6.  RE: Large IO block size (writes / read), High latency..

    Posted Sep 22, 2012 10:46 AM

    i found out that disabling jumbo frames on a intel card solves the problem.

    I also tried it with a broadcom adapter and i had no problem what so ever.