You may need it for example for an firmware upgrade of the disks on the storage system. Please ensure that you don’t have huge IO in the time frame and you applications will not timeout because of missing disk and will retry disk IO operations.
From the official VMWare documentation
Setting the HBA Timeout for Failover The timeout value for I/O retry operations is usually set in the HBA BIOS driver. (You might also want to change the operating system timeout, as discussed in “Setting Operating System Timeout” on page 148.) VMware recommends that you set the timeout value to 30 seconds: For QLogic HBAs, the timeout value is 2*n + 5 seconds, where n is the value of the PortDownRetryCount parameter of the BIOS of the QLogic card. You can change the path-failure detection time by changing the value of the module parameter qlport_down_retry (whose default value comes from the BIOS setting). The recommended setting for this parameter is 14. For Emulex HBAs, you can modify the path-failure detection time by changing the value of the module parameters lpfc_linkdown_tmo (the default is 30) and lpfc_nodedev_tmo (the default is 30). The sum of the values of these two parameters determines the path-failure detection time. The recommended setting for each is the default. To change these parameters, you must pass an extra option, such as qlport_down_retry or lpfc_linkdown_tmo, to the driver.
Preparation of the ESX-Hosts
- Migrate all VM’s to the other active nodes. Go into maintenance mode.
- Login via ssh and configure the timeout(QLogic HBAs):
esxcfg-module -s qlport_down_retry=300 qla2xxx.o
- you can show the actual options with
esxcfg-module -g qla2xxx.o
- Reboot the host and leave the maintenance mode.
- Do this with all ESX-Hosts in the environment.
After that you can start the firmware upgrade. In the tests, the system was running fine without a storage approximately 10 minutes.