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John Sansom
Asked: 2009-09-20 03:15:12 +0800 CST

Best use for new 10K RPM Hard Disk - OS Location or VMware vmd's

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Purchased a 10k RPM Velociraptor 300GB Hard Disk with the intention of using it to store my VMWare Workstation virtual machine disks.

However I am now wondering whether I will see more overall performance improvement by using it to store the primary OS (Windows 7). Currently the OS is on an older 7.2k rpm drive.

What do you think would be the best course of action?

vmware-workstation

5 Answers

  1. It really depends on how your work load is setup. Assuming you have enough ram to each of the VMs, the OS will see a bigger benefit from the 10k drive. If you are working inside of the VMs, and you have less RAM, storing the VMs on the drive will show the improvement. This is due to the way the swap access works.

    While the VM will be swapping to disk, the actual disk access could be coming from memory if the host OS has enough ram to cache the physical disk access.

    VM Reads from Disk
Host OS process command
if Data stored in Host Disk Cache
 return from memory
else
 read from physical disk`
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  2. Best Answer

    Having just recently gone through the experience of replacing the drive used for my VMWare drive images, I've learned a few things. First thing, a creeping bad cluster problem makes for a poor VMWare drive, thus the move. Second, Native Command Queuing did very noticeable things in making my VM's respond more snappy.

    When I first made the drive NCQ wasn't common on all drives yet, though these days most have it. On digging into the I/O subsystem (Linux, so this was a bit easier than Windows) I found that the average queue wait times were markedly lower under similar loads, which is a factor of a couple things one of which is disk latency. A 10K drive would scale further than the 7.2K drive I have. It'll still hit performance bottlenecks at some point, even with NCQ, but it'll take longer.

    Which is to say, if you're already experiencing I/O bottlenecks with the VMs you're already running, that 10K drive will help. It'll help even more if it has NCQ and the old drive does not. In my case, on my old 7.2K drive w/o NCQ booting two Vista VM's at the same time was enough to send the average queue wait times through the roof. With NCQ, wait times are elevated but reasonable.

    As for OS vs. VM, I'd lean VM. Windows is smart enough to allow I/O contention on one SATA drive to not significantly get in the way of other SATA drives. Also, if you're doing workstationy things with that OS drive, like run Outlook and do your day to day tasks on it, it'd take an unusual workload to make it wiser to put the 10K drive on the OS side rather than the VM side. In my experience VM I/O loads are random enough that it deserves the more expensive kit.

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  3. When you're running VMs, the OS disk is almost never accessed; so you really should use the faster disk for VM storage.

    Even if your host needs to swap a lot (which I hope it doesn't), VMs will still probably do a lot more disk I/O than the host, especially if you run two or more of them.

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  4. Depends. I love that answer because it's usually right but is absolutely of no help. Like most tech support lines :-)

    The answer is, what are you doing with your VM's? If you're doing disk reads all the time, put them on the 10k. If you're suitably outfitted with memory, it's not such an issue. If you're doing most disk reads with your primary OS, put that on the 10k drive.

    Bump your memory up and you'll see an improvement either way. If you're doing something where in casual use you're actually going to sit back and whistle in amazement at saving a couple minutes reading a really really big file then you should know which way to set it up already because you're already doing something that bogs down disk reads and writes, like video editing.

    Otherwise reading a word document is pretty much not going to matter too much if it's a 10k or 7.5k drive. In average use, it averages out. Unless your addicted to benchmarks, of course, in which case you should already be planning to up your system to 32 gig and a new motherboard and finding the stats to see if RAID 1 is going to boost your read speeds enough to load up that file in 1.2 seconds instead of 2.3 seconds :-)

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  5. Maybe you should partition the 10K RPM drive into two partitions and put your VMs on one partition and your host's swap file on the other partition?
    If you were using ESX, then then the best practice is that the VMs get the 10K RPM drive.
    BTW, if you are really concerned about performance in a VM situation, you really should run ESX or ESXi (which is free)

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