ClearCube A1010 Uživatelský manuál stáhnout pdf (Strana 6)

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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

i. ESX optimization

This ESX memory pattern matching and swapping

algorithm improves over time on an individual ESX

installation. As users access and use the same ap-

plications, ESX will more frequently swap out the

common applications from memory. As the users

continue to access the system with similar applica-

tions over time, overall system memory utilization

will decrease, resulting in improved system perform-

ance over time. Within 24 hours of system usage,

the ESX kernel has evaluated and balanced overall

memory usage to derive an optimized congura-

tion. Although numerous CPU cycles are required

to achieve this efciency, the feature works consist-

ently to enhance system performance over time.

ii. ESX memory utilization considerations

Unfortunately this overall system efciency is “re-

set” once the main ESX server is rebooted. Be-

cause the memory-matching algorithm is dynamic,

ESX cannot predict and maintain memory utilization

footprints between reboots. Once a server reboot

occurs, the ESX kernel will reevaluate memory uti-

lization and start swapping out memory as it recog-

nizes common memory patterns making it possible

to “over-subscribe” the memory (i.e. 12 VMs in a 6.0

GB RAM system).

This over-subscription takes time to become effec-

tive. If a 13th VM is added, the overall system slows

to accommodate the new VM. Similarly, a 14th VM

can be added, but the overall system is slow for a

period of time as the ESX kernel makes memory ad-

justments. For an R2200 with 6 GB RAM, a congu-

ration with 12 VMs will load and run efciently after

a reasonable period of time following a reboot. The

amount of time it takes to readjust varies based on

system load in the VMs. If all the VMs are quies-

cent, the memory adjustments to add an additional

VM can occur in less than 20 minutes. If all the VMs

are fairly active, then full memory readjustment may

require up to 36 hours. As more VMs are congured

into a system, the reboot readjustment period will

generally take proportionately longer time periods.

This point should be heavily weighed when evaluat-

ing new installations of ESX in a corporate environ-

ment. If you have very stable power, rarely experi-

ence power outages, and have similar workloads,

you may consider establishing a conguration with

the maximum VMs for a given memory conguration

(i.e. 14 VMs for 6 GB). However, if you reboot your

ESX server during work hours, users on that ESX

server may experience up to 30 minutes of outage

as the system reboots and re-establishes the basic

memory efciencies. Conguring maximum VMs per

server should be considered only if you have a very

stable environment and perform hardware mainte-

nance on weekends.

GB RAM/VM Total GB Purpose

0.5 0.5 Used by VMware ESX3

0.5 6.0 Required for 12 x 512MB RAM used by each VM

6.5 Theoretical memory usage by the system

6.0 Actual memory used for the whole system

Table 4. Memory Requirement for R2200 Virtual Machines

1 2 3 4 5 6 7 8 9 10 11 12

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