VMware just published a very interesting study about how many I/O Operations per Second (IOPS) an ESX 3.5 Update 1 can perform.
To perform the measurement they used a unnamed server with 4 Intel quad-core CPUs and 32GB RAM, plus 2 dual-port QLogic 4GB HBAs and 2 single-port QLogic 4GB HBAs.
The backend storage was made of 3 EMC-CLARiiON CX3-80 (a Fibre Channel SAN) with a remarkable number of 495 disks, serving more than 77TB data.
After fine tuning the system with the following three settings, the IOMeter test returned a result of over 100,000 IOPS:
- We increased the VMFS3 max heap size from 16MB to 64MB (KB article # 1004424).
- We changed the storage processor’s cache high/low watermark from 80/60 to 40/20. This was done to write the dirty pages in storage cache more often so that Iometer write operations do not wait for free memory buffers.
- We increased the guest queue length to 100 to make sure that the guest was capable of queuing all the I/O accesses generated by IOMeter to the test disks.