VMware I/O performance – Guest vmdk vs Guest iscsi initiator

Today i decided to run some I/O benchmarks within a VMware environment to compare a performance of a virtual disk assigned to a virtual machine vs a disk accessed by an iscsi initiator.

Basically the VM had 2 virtual disks assigned for the benchmark :

1. Disk E is a thick virtual disk added from VMware. This vmdk resides on a SAS based datastore ;
2. Disk F is a disk accessed by the iscsi initiator from Windows. This disk is served from a Dell Equallogic PS6000 and MPIO is enabled
3. The disk controller it’s the LSI Logic SAS provided by VMware

Results : ( results parsed at http://vmktree.org/iometer/ )

• I/O using the ISCSI Initiator from Windows

Test name	Latency	Avg iops	Avg MBps	cpu load
Max Throughput-100%Read	0.00	6380	199	33%
RealLife-60%Rand-65%Read	12.16	4244	33	9%
Max Throughput-50%Read	78.83	4812	150	45%
Random-8k-70%Read	10.16	4142	32	9%

• I/O using the assigned virtual disk

Test name	Latency	Avg iops	Avg MBps	cpu load
Max Throughput-100%Read	0.00	7183	224	26%
RealLife-60%Rand-65%Read	12.05	4208	32	10%
Max Throughput-50%Read	111.94	6833	213	26%
Random-8k-70%Read	9.38	3817	29	9%

Conclusion :

The virtual disk outperforms the iscsi disk for read loads and has a slight less performance for random workloads . Interesting that when the virtual disk performance is lower we see a high CPU usage as well on the VM.Something to be investigated…..

Unless your environment needs an iscsi connection , for instance for hosting MS Clusters, the performance of a virtual disk it’s quite good as well , with all the advantages of snapshot, svmotion, etc..

Environment configuration details :

VMware Infrastructure configuration :

• VMware ESXi 4.1 Update 1
• Dell R515 with 2 sockets AMD Opteron 4180 (2.6GHz) with 64GB
• Equallogic PS6000 with 15 600GB 15K rpm SAS disks with 1 volume assigned to the VM and one provisioned as a datastore within VMware
• iscsi switches based on 2 Dell PowerConnect 6224 stacked
• 2 networks configured within VMware to access the Equallogic . Each network has 2 Intel 82576 gigabit cards allocated.
• Jumbo frames are enabled on Equallogic, switches, vswitches

Client configuration :

• Windows 2008 R2 (64bits) Enterprise Edition
• 2 vCPU
• 2GB memory
• 2 virtual network cards assigned for storage traffic , based on VMXNET3 , with Jumbo Frames enabled on the OS
• Dell Equallogic Host Integration Tools installed and MPIO enabled
• I/O benchmark done with IOMeter (1.1.0-rc1-win64.x86_64) using the OpenPerformanceTest.icf file .
• For extra results check out  the VMware unofficial storage performance thread