Disk.UseLunReset and/or Disk.UseDeviceReset

A setting often overlooked is Disk.UseLunReset and/or Disk.UseDeviceReset. ESX defaults to Disk.UseLunReset=1 and Disk.UseDeviceReset=1. This means that when a SCSI bus is reset all SCSI reservations are cleared, not for a specific LUN but for the complete device. This is useful when one uses local storage, but within a VMware environment most companies utilize a SAN and you don’t want to disrupt the entire SAN when it’s not necesarry. You can set this via the commandline, powershell and via VirtualCenter:

  1. VirtualCenter -> Configuration Tab -> Advanced Settings -> Disk -> Disk.UseLunReset=1 , Disk.UseDeviceReset=0
  2. Get-VMHost | Set-VMHostAdvancedConfiguration -Name Disk.UseDeviceReset -Value 0
  3. Commandline -> esxcfg-advcfg -s 1 /Disk/UseLunReset

    Commandline -> esxcfg-advcfg -s 0 /Disk/UseDeviceReset

After setting this you need to reboot the ESX server with the following command :

esxcfg-boot -b

Source : http://www.yellow-bricks.com/2008/07/21/queuedepth-and-whats-next/

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