Specifications

Administration Guide
348 VMware, Inc.
Swap!space!must!be!reserved!on!disk!for!the!remaining!virtual!machine!memory—that!
is!the!difference!between!the!maximum!and!minimum!settings.!This!swap!reservation!
is!required!to!ensure!the!system!is!able!to!preserve!virtual!machine!memory!under!any!
circumstances.!In!practice,!only!a!small!fraction!of!the!swap!space
!may!actually!be!used.!
Similarly,!while!memory!reservations!are!used!for!admission!control,!actual!memory!
allocations!vary!dynamically,!and!unused!reservations!are!not!wasted.
The!amount!of!swap!space!configured!for!the!system!limits!the!maximum!level!of!
overcommitment.!A!default!swap!file!size!equal!to!the!physical!memory!size!of
!the!
computer!is!recommended!in!order!to! support!a!reasonable!2x!level!of!memory!
overcommitment.!You!may!configure!larger!or!smaller!swap!files!or!add!additional!
swap!files.!
If!you!do!not !configure!a!swap!file,!memory!may!not!be!overcommitted.!You!may!
configure!the!swap!file!using!the!VMware!
Management!Interface!(Swap!Configuration!
in!the!Options!page)!or!from!the!service!console!using!the!vmkfstools!command.!
You!can!create!additional!swap!files!using!the!vmkfstools!command.!You!should!
consider!adding!additional!swap!files!if!you!want!to!run!additional!virtual!machines!
but!you’re!unable!to!do!so!because!of!
the!lack!of!swap!space.!See!“Using!vmkfstools”!
on!page 249.
Allocating Memory Dynamically
Virtual!machines!are!allocated!their!maximum!memory!size!unless!memory!is!
overcommitted.!When!memory!is!overcommitted,!each!virtual!machine!is!allocated!an!
amount!of!memory!between!its!minimum!and!maximum!sizes.!The!amount!of!memory!
granted!to!a!virtual!machine!above!its!minimum!size!can!vary!with!the!current!memory!
load.
!The!system!determines!allocations!for!each!virtual!machine!based!on!two!factors:!
the!number!of!shares!it!has!been!given!and!an!estimate!of!its!recent!working!set!size.
ESX!Server!uses!a!modified!proportional‐share!memory!allocation!policy.!Memory!
shares!entitle!a!virtual!machine!to!a!fraction!of!physical!memory.
!For!example,!a!virtual!
machine!that!has!twice!as!many!shares!as!another!is!entitled!to!consume!twice!as!much!
memory,!subject!to!their!respective!minimum!and!maximum!constraints,!provided!that!
they!are!both!actively!using!the!memory!they!have!been!allocated.!In!general,!a!virtual!
machine!with!S!memory!
shares!in!a!system!with!an!overall!total!of!T!shares!is!entitled!
to!receive!at!least!a!fraction!S/T!of!physical!memory.
NOTE To!create!SMP!virtual!machines!with!ESX!Server,!you!must!also!have!purchased!the!
VMware!Virtual!SMP!for!ESX!Server!product.!For!more!information!on!the!VMware!
Virtual!SMP!for!ESX!Server!product,!contact!VMware,!Inc.!or!your!authorized!sales!
representative.