Specifications

VMware, Inc. 265
Chapter 9 Storage and File Systems
can!immediately!access!the!necessary!data!when!the!failover!occurs.!See!
“Configuration!for!Clustering”!on!page 279!for!information!on!clustering!with!ESX!
Server.
The!bus!sharing!setting!is!used!to!determine!whether!virtual!machines!are!allowed!to!
access!the!same!virtual!disk!simultaneously.!
Setting Bus Sharing Options
Use!the!VMware!Management!Interface!to!change!the!bus!sharing!settings!for!each!
virtual!machine!that!will!access!the!same!virtual!disk!simultaneously.!
There!are!three!bus!sharing!options:
! None!–!Disks!cannot!be!shared!by!other!virtual!machines.
! Virtual!–!Disks!can!be!shared!by!virtual!machines!on!same!server.
! Physical!–!Disks!can!be!shared!by!virtual!machines!on!any!server.
To!enable!sharing!of!virtual!disks,!choose!Virtual!or!Physical.!All!virtual!disks!on!the!
specified!virtual!bus!will!be!sharable!and!have!the!specified!mode.!
! Virtual!bus!sharing!–!Only!virtual!machines!on!the!same!physical!machine!will!be!
able!to!share!disks.!This!setting!allows!for!a!“cluster‐in‐a‐box”!configuration,!in!
which!all!members!of!a!high‐availability!cluster!are!on!the!same!physical!machine.!
This!setup!is!useful!for!providing!high!availability
!when!the!likely!failures!are!due!
to!software!or!administrative!errors.
! Physical!bus!sharing!–!Virtual!machines!on!different!physical!machines!will!be!
able!to!share!disks.!In!this!case,!the!VMFS!holding!the!virtual!disks!must!be!on!a!
physically!shared!disk,!so!all!of!the!physical!machines!can!access!it.!This!setup!is!
useful!for!providing!high!availability!when!the
!likely!failures!also!include!
hardware!errors.
When!a!shared!disk!is!used!for!high!availability,!the!current!machine!running!the!
application!and!using!the!shared!data!often!reserves!the!disk!using!a!SCSI!command.!
Also,!if!the!bus!sharing!is!Physical,!commands!that!reserve,!reset!or!release!a!shared!
virtual!
disk!are!transmitted!through!to!the!physical!disk,!so!other!machines!sharing!the!
disk!can!properly!detect!when!a!virtual!disk!has!been!reserved!or!reset.!
When!you!are!sharing!disks!among!virtual!machines!across!physical!machines!for!high!
availability!purposes,!it!is!often!best!to!put!only!a!single!VMFS
!with!a!single!virtual!disk!
on!each!shared!disk,!that!is,!have!only!one!virtual!disk!per!physical!disk.!In!such!a!
configuration,!each!virtual!disk!can!be!reserved!and!released!independently.