Software iSCSI Targets: Part 2B – StarWind, Multiple VMs

Part 2B: 3 VM IOMeter load on a StarWind iSCSI datastore. Same procedure as previous testing – Complete install time: 32 minutes, 39 seconds – 3.5 minutes faster than the Microsoft iSCSI target software. Here’s the setup:

Here’s the CPU\RAM of the iSCSI server during OS install:

Just as previously, RAM is allocated to cache and CPU is heavily utilized. Here is the network utilization during OS install:

The utilization graph looks strikingly similar to the MS iSCSI target install, however, utilization goes over 30% at a few points. During the major portion of OS install – CPU utilization is high, as is the underlying physical disk queue length. This shows me that a faster disk subsystem would improve performance even further.

And a brief view of network utilization during VMWare tools install on all 3 VMs:


Deduplication and Thin Provisioning

StarWind clearly has the advantage here. Not only is the LUN thin provisioned, but it is also deduped once data is written. The deduplication engine works inline, so as data is being written, it is deduped – with a 4K size, it is very effective. All 3 VMs should be taking up nearly 27GB of space – but as you can see, they are not – only about 8.69GB of used space. This yields a 3.15:1 dedupe ratio – which is what I would expect for 3 mostly identical servers.


*Note: Each VM should be taking up about 9.13GB however, there is likely some block redundant data within the IOMeter test files on each VM.


Performance – Single VM IOMeter, 2 VMs Idle

Again, the StarWind iSCSI target showed far better performance than the Microsoft software target:

I also tested rebooting one of the idle VMs while this test was running – as expected the IOPS dropped down to the 300 range, and response time went up. The physical disk queue also jumped – again showing this as a limitation (reboot initiated at 11:09 AM).


All 3 VMs running IOMeter

With all 3 VMs running an IOMeter worker, the performance is still very good. Keep in mind that the IOMeter test files are 500MB – the 3 combined likely fit in the StarWind cache helping the test along. Only 2 of the 3 VMs shown:

The network utilization as the 3 tests are started:



The StarWind iSCSI target software has several clear advantages over the Microsoft solution – performance advantages including high-speed RAM cache, thin provisioning, deduplication…with a high-performance disk subsystem that includes controller-based RAM cache as well as faster physical spindles – a major performance boost can be had. Additionally, aggregating network links and adding more RAM to the cache can produce a powerful, fast and efficient software based iSCSI storage solution.

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