There's no need to turn off the SAN, just remove the host from the Storage Group (that's for an EMC-SAN, there should be a similar term if your SAN is another brand), or unplug the fibre-cables...
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There's no need to turn off the SAN, just remove the host from the Storage Group (that's for an EMC-SAN, there should be a similar term if your SAN is another brand), or unplug the fibre-cables. Do the upgrade, then reconnect the cables (or add the host to the Storage Group). That way you're safe. If you're doing a new install it's always considered best practice to disconnect the host from the SAN, as the installation can go a bit wrong if you don't. For instance, the first disk should always be named /dev/sda, but if you're doing a new installation with the SAN connected you might end up with something like /dev/sdf, which could result in weird concequences. So in any way, you'd be better off disconnecting the host from the SAN