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P e r f o r m a n c e W h i t e P a p e r

In the A1010 example with 3 GB RAM, if a sixth VM

is congured and started, the whole system slows

to a crawl. There is no memory sharing between

the VMs. The VMware kernel + MS Server 2003 re-

quires the full 512 MB of RAM in order to properly

accomplish its task. You cannot “over-subscribe” the

memory. What you install and congure is what you

get!

If a sixth VM is installed, the system will try to accom-

modate the new VM by temporarily swapping out the

allocated memory for one of the rst ve VMs. This

faulty conguration will temporarily turn off one VM

(an ofce user); the memory is used for the recently

added sixth VM. This is not a reasonable congura-

tion.

b. R2200 + VI-3 (ESX) Conguration

For this study, the R2200 was congured as shown

in the following gure. ESX is typically setup to run

on one machine and the storage for the VMs is setup

to run on IP-based storage. VMs are accessed over

a standard Ethernet switch. Here, NFS was setup

using Suse Linux on an R1300. The local hard disk

on the R1300 acted as a NAS (Network Attached

Storage) device. There was no noticeable I/O degra-

dation during any of the testing with ESX, and a sub-

sequent set of tests using a commercial iSCSI SAN

product did not visibly improve I/O performance.

Consider an R2200 blade with 6 GB of RAM. This

conguration can easily support 12 VMs in a typical

ofce worker situation. Using a sophisticated mem-

ory algorithm, ESX allows VMs to “over-subscribe”

the physical memory in a system. ESX will use ap-

proximately 512 MB of RAM to run the ESX kernel.

If each of the remaining VMs used 0.5 GB RAM as

they did with VMware Server 1.0.1, the overall utili-

zation would be 6.5 GB of RAM.

In this R2200 example, 12 VMs are able to run be-

cause of the over-subscribed memory. ESX evalu-

ates the memory usage pattern of each VM. If the

ESX kernel nds two exact copies of the same con-

tent (i.e. Microsoft Word application) in memory, it

swaps out one of those copies. This frees memory

to be used by other applications or VMs.

As a result, if each of the 12 VMs is running the

exact same copy of Microsoft Word, only one copy

of the application stays resident in memory and the

remaining 11 copies are swapped out of memory.

(The content of the 12 Word documents will re-

main in memory since each document is likely to be

unique.)

Fig 1. R2200 + VI-3(ESX) Conguration

Network

Switch

VMware VI-3 ESX

SUSE Linux + NFS

R2200

R1300

I/Port

Win XP

Suse Linux Hard Drive

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