DB2 and vSphere 4 limit of 8 vCPU

04 April,2012 by Tom Collins

 Question. In vSphere 4.1 there’s a limit of 8 virtual cores per guest. If the host has 24 cores available – and I have only one other Virtual Machine(VM) using 8 virtual cores – how can I utilise the remaining 8 cores?.

 Host – 24 cores

VM1 – 8 Cores

VM2  - 8 cores



Answer 8  virtual cores means you’ll never have more than 8 threads executing in parallel on the VM.

vSphere uses a queue structure for CPU resources, dispatching work to processors as required.  Once the work is processed , it’s reassembled and returned to  the vCPU. ESX does the work of reassembling the multiple work units.

DBA perspective –  highly iterative and closely aligned tasks are suited to this architecture. Application architecture examples include Process Servers.

Queries requiring complex instruction sets with high levels of earlier instruction dependancy are not as suited.

The DBA must answer the question Is Virtualization a viable alternative?

The main difference between UNIX and ESX CPU Schedulers is how processor priority is decided. In UNIX , it’s  based on user choice. In ESX, the decision is based on actual usage and “entitlement” , such as reservation, shares and limit


In a all cases – testing is important – with load testing tools such as nmon - tuning and benchmark tool  and DB2 and Linux IO testing tools

Author: Rambler(http://www.dba-db2.com)


Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment on DB2 and vSphere 4 limit of 8 vCPU

Comments are moderated, and will not appear until the author has approved them.

dba-db2.com | DB2 Performance Tuning | DBA DB2:Everything | FAQ | Contact | Copyright