Installing VMware Tools in a Windows or Linux VM increases the I/O timeout for all disks to help the guest OS survive a short SAN/NAS storage outage.

If you wish to increase this value from the VMware default ( or if you don’t install VMware tools for some reason), there are couple ways to automate this. Jason McCarty last week posted a nice PowerCLI script to automatically set Windows Guest timeout registry setting to the NetApp recommended value of 190 seconds:http://www.jasemccarty.com/blog/?p=691.

If you are running RHEL5 with vSphere U1 VMware tools installed, the default is set to 180 seconds in /etc/udev/rules.d/99-vmware-scsi-udev.rules. You can increase this if you want by editing this file, or manually set /sys/block/sda/device/timeout in /etc/rc.local to avoid a VMware tools upgrade from changing your settings.