Installation guide

C H A P T E R 1 0 Configuration for Clustering
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In a public VMFS-2 volume, locking is at a per-file level, resulting in fewer locking
issues. However, you may still encounter the preceding message and may need to use
vmkfstools --recover, if a server fails.
If a VMFS is used to store a virtual disk that is accessed by multiple virtual machines on
multiple physical servers for the purposes of failover clustering, the VMFS should be
configured as a shared file system. Then, the locking protocol is slightly relaxed to
allow multiple virtual machines on different servers to access the same VMFS file at
the same time. However, file system commands do the same locking as with public
file systems (that is, per-VMFS in VMFS-1 volumes and per-file in VMFS-2 volumes).
Additionally, when multiple virtual machines access the VMFS, the VMFS file system
enters a read-only mode in which it is impossible to create, delete or change the size
of files. However, the contents of the individual files can still be modified. If you later
want to create or remove VMFS files, you must stop all virtual machines using the
VMFS and re-enter writable mode by using this command:
vmkfstools --config writable vmhba0:1:0:0
Substitute the name of the appropriate disk or VMFS in place of vmhba0:1:0:0.
Locking at SCSI Disk Level
The second kind of locking is locking at the SCSI disk level, which is called SCSI disk
reservation.
Any server connected to a SCSI disk can issue a SCSI command to reserve the disk. If
no other server is already reserving the disk, the current server obtains a reservation
on the disk. As long as that reservation exists, no other server can access the disk. All
SCSI commands to that disk by other servers fail with an appropriate error code.
If a vmkfstools command is attempted on a VMFS on a disk that is reserved by
another server, the vmkfstools command fails with a message that says:
vmkfstools: shared SCSI disk is reserved by another
server. Use 'vmkfstools -L release/reset' to end
reservation if no other server is using the SCSI
reservation
Similarly, a virtual machine fails to start if its virtual boot disk is stored on a physical
disk that is reserved by another host.
Most applications do not ever reserve a SCSI disk. However, failover clustering
software reserves SCSI disks in order to ensure that only the active node is able to
access the shared SCSI disk. Therefore, you should expect that the shared disk in a
physical clustering setup is reserved when the cluster is active. Similarly, for a virtual