Why no speed increase inside VM after installing a faster SSD?

[mfcmfc]

In my 2011 MacBook Pro that supports SATA 6Gb/s I switched from
Intel X25M G2 SSD 160GB 3Gb/s
To
Patriot Wildfire 240GB 6Gb/s (equivalent to OCZ Vertex Max IOPS)

In the Mac benchmark program, XBench, the disk speed sees a dramatic increase. Inside of VMWare Fusion, the benchmark programs indicate no speed increase, and even a slight speed decrease. The Windows benchmark programs I am using are PassMark, ATTO, and CrystalDisk.

Does anyone know why my VMWare instance is not seeing any noticeable speed increase after swapping in a hard drive that is over 3x the speed of the original drive?

The benchmark programs are reporting speeds of around 650MB/s for both the Intel drive and the Patriot drive for both sequential read and write speeds. These speeds are faster than either drive is capable of, so it seems what is being measured is the effectiveness of caching performed by VMWare. For the random read speeds, the Intel drive measures 40MB/s and the faster Patriot drive measures 30MB/s.

I use my VMWare instance for making Web applications using Visual Studio, checking E-mail, and other work-related activities, and I do not notice any speed difference with the faster drive, in agreement with the benchmark programs. My VMWare instance is around 90GB and I am inside the VM around 99% of the time while on the Mac.

[a_p_]

Which Windows OS are you using? If it is Windows XP (or earlier) you may have an unaligned partition layout which causes the decreased performance on the SSD. You may check whether the partition offset is a multiple of 32kb (Windows Vista and newer use 1.024 kb) using e.g. msinfo32.exe.

André

[mfcmfc]

I am using Windows XP SP3 32bit running on Mac OS 10.6.8 and VMWare Fusion 3.1.3 . I didn't think partition alignment was an issue within a VM.

[mfcmfc]

This is my partition alignment:

Partition ###  Type              Size     Offset
-------------  ----------------  -------  -------
Partition 1    Primary             81 GB    32 KB
Partition 2    Primary             23 GB    81 GB

So my VM hard drive does not appear to be aligned. I am assuming there isn't much I can do to easily fix this. I'm not sure how much this impacts the speed though. I know aligment is very important for the base operating system, but the VMWare hard drive should be abstracted from the physical hard drive.

[mfcmfc]

Using wmic:

BlockSize  Index  Name                   StartingOffset
512        0      Disk #0, Partition #0  32256
512        1      Disk #0, Partition #1  86957660160
512        0      Disk #1, Partition #0  28672

[WoodyZ]

Both the physical and virtual disks need to be aligned especially with a Windows XP Virtual Machine.

I always pre-partition/format my Windows XP HDD's with GParted Live because it automatically creates an offset at 1MB which is then aligned.  I've also used it after the fact to move a partition into alignment.  There is also Paragon Alignment Tool 3.0.

[mfcmfc]

I performed some optimizations:

Updated the VMWare tools to the lateset version.

Moved the OS from a nearly full 80 GB dynamic hard drive to a new 100 GB preallocated drive with the correct partition alignment.

Created a new drive for the paging file that was correctly aligned.

The alignment change does seem to help. The problem now is that when I run that benchmark program, which I have run dozens of times over the years on this VM, it crashes consistenly on the sequential read disk test. When I say crash, the Mac's CPU spikes all the way up and stays there until I shut down the VM. I tried this benchmark program three times and it failed to complete in the same way every time, so I stopped trying and I don't have a new score to compare to my prior score. I am using the VM for normal work though.

I discovered the setting to disable buffering of the drive, which results in more accurate drive speed measurements when I do benchmarks inside the VM. The problem with disabling buffering, however, is that the Mac gets a kernel panic and shuts down every time before the test completes. It is a 100% reproducable problem, and it happened before and after I did the above optimizations. I didn't try disabling disk buffering with my old Intel SSD, so I'm not sure whether it is a problem with my new drive or not. I have read other posts on this forum suggesting that VMWare Fusion has problems with disk buffering disabled.