Specifications

VMware, Inc. 371
Chapter 12 VMware ESX Server Resource Management
Managing Disk Bandwidth
ESX!Server!provides!dynamic!control!over!the!relative!amount!of!disk!bandwidth!
allocated!to!each!virtual!machine.!You!can!control!disk!bandwidth!separately!for!each!
physical!disk!or!logical!volume.!The!system!manages!the!allocation!of!disk!bandwidth!
to!virtual!machines!automatically!based!on!allocation!parameters!and!system!load.!This!
is
!done!in!a!way!that!maintains!fairness!and!tries!to!maximize!throughput.
You!can!specify!initial!disk!bandwidth!allocation!values!for!a!virtual!machine!in!its!
configuration!file.!You!can!also!modify!disk!bandwidth!allocation!parameters!
dynamically!using!the!VMware!Management!Interface,!the!procfs!interface!on!the!
service!console,!or!the
!VMware!Scripting!API.
Reasonable!defaults!are!used!when!you!do!not!specify!parameters!explicitly.!To!run!a!
virtual!machine!that!will!have!disk‐intensive!workloads,!such!as!a!database,!or!file!
server,!you!might!want!to!increase!its!disk!shares.
Information!about!current!disk!bandwidth!allocations!and!other!status!is!available!
through!the!management!interface,!the!procfs!interface!on!the!service!console,!and!the!
VMware!Scripting!API.
Allocation Policy
ESX!Server!uses!a!modified!proportional‐share!allocation!policy!for!controlling!disk!
bandwidth!per!virtual!machine.!This!policy!attempts!to!control!the!disk!bandwidth!
used!by!a!virtual!machine!to!access!a!disk!while!also!trying!to!maximize!throughput!to!
the!disk.!
Disk!bandwidth!shares!entitle!a!virtual!machine!to!a
!fraction!of!the!bandwidth!to!a!disk!
or!LUN.!For!example,!a!virtual!machine!that!has!twice!as!many!shares!as!another!for!a!
particular!disk!is!entitled!to!consume!twice!as!much!bandwidth!to!the!disk,!provided!
that!they!are!both!actively!issuing!commands!to!the!disk.!
Bandwidth!consumed!
by!a!virtual!machine!is!represented!in!consumption!units.!Every!
SCSI!command!issued!to!the!disk!effectively!consumes!one!unit!by!default!and!
additional!units!proportional!to!the!size!of!the!data!transfer!associated!with!the!
command.
Throughput!to!the!disk!is!maximized!through!the!use!of!a!scheduling!quantum!for!
disk!
requests!from!a!virtual!machine!to!a!disk.!A!virtual!machine!is!allowed!to!issue!a!
number!of!requests!to!a!disk!(the!scheduling!quantum)!without!being!preempted!by!
another!virtual!machine.!The!issuing!of!a!multiple!requests!without!preemption!is!
applicable!only!if!these!requests!access!sequential!sectors!on
!the!disk.