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LUN suddenly becomes unavailable to one or more ESX Hosts

A LUN becomes unavailable to many of the ESX hosts.
Virtual machine can give the error when trying to power on:

Can't find the config file and are not accessible

The LUN of the affected datastore is locked by one of the ESX hosts. Typically, there is nothing queued for the LUN.

These procedures help release the lock.

ESX 3.0

To force a release of the reservation, use the command:

vmkfstools -L lunreset /vmfs/devices/disks/vmhbaX:X:X

ESX 4.0

Note: In these examples, the device that has the problem is located at /vmfs/devices/disks/naa.600601604b901c0076ee59af2b36de11.

Generate some I/O to the affected LUN:
dd if=/vmfs/devices/disks/naa.600601604b901c0076ee59af2b36de11 of=/dev/null count=1024
All of the hosts except one should show dozens of messages in VMkernel logs like:
naa.600601604b901c0076ee59af2b36de11: Sync CR (opcode 28) at 64 (wid 544)
One of the hosts does not have the errors. This is the host that has the lock on the LUN. Perform a LUN reset to clear the lock from this host.

vmkfstools -L lunreset /vmfs/devices/disks/naa.600601604b901c0076ee59af2b36de11

The LUN is now accessible from all hosts.

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