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chickeninabiscuit
Asked: 2009-05-29 01:18:41 +0800 CST

Would my VM (winxp) perform better if the disk images were stored on a 5.4k drive over SATA, or an external 7.2k SATA drive over USB2?

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My laptop has a 5.4k drive - plus i have an external 7.2k drive. Where to put the vm... hmmm?

Has anyone faced this dilemma?

If not I'll post my results.

Ash

virtualization performance

5 Answers

  1. I'd go with the external drive. Not because it's 7.2k vs. 5.4k, but because it's a different drive than your operating system drive (that is assuming your laptop only has one hard drive, which is the 5.4k in question).

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  2. Almost certainly it'd perform better using the SATA drive. USB has quite a slower latency - 100 microseconds compared to 0.5 for PCI.

    The disk speed won't matter so much so if you're reading and writing large files, you're not interested in seek times for small files, the burst time taken to fill an read from the buffers will be more important than the speed of the drive.

    Now, if you had an attached 15k SAS RAID array, that's be another story. I'm not sure you'll notice too much of a difference whichever you choose.

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  3. A colleague who is a technical sales person, found on his Dell laptop that getting an SSD as a disk to host VM's for demos, using the CD/DVD drive bay with an adapter (So I assume it is PATA at least, if not SATA, rather than USB, or maybe it is USB? Don't really know) was a huge performance booster.

    The nice thing is that if you get a second drive, a USB enclosure is about $10. So the experiment is pretty cheap, and if it fails, you can always swap the new drive for you current internal to boost performance overall, and still have a spare USB drive.

    I foolishly swapped my internal 100GB 7200 rpm SATA drive for a 300GB 5400 rpm SATA drive and I am currently deeply regretting it. Performance is very noticeably slower. If I did not absolutely require the extra space, I would move back to the 7200 drive in a moment!

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  4. Personally I'd go with the 5400 option only for the fact that when using a laptop I do not want to have to plug stuff into it (extra drive = extra weight, usb = more power draw on battery too).

    You could swap the 5400 and 7200 drives around as another option.

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  5. If you won't have I/O intensive processes in host system fighting with VM, I recommend going with internal drive (unless external is for convenience/space). USB2 simply can't deliver.

    If you want speed, I'd recommend avoiding USB2 - it's slow, sometimes very. If you want to really exploit usage of external hard drive, I recommend getting an eSATA card (or FireWire, especially 800MBit, but it's rare to find SATA bridge for it).

    USB is a polled interface and doesn't really support anything like DMA, so I can guarantee that you'll never see those promised 480MBit speeds :)

    Long time ago, testing the same, old drive in a dual USB2/FireWire enclosure (a 5400rpm UltraATA133 drive, nothing fancy), I recorded sustained speeds of >30MB/s on FireWire, with USB2 baseline being somewhere around 10~15MB/s (initial speed ~30MB/s, then fast drop).

    Lately, similar experience except with modern drive, modern USB2->SATA2 controller vs. eSATA card - do I need to say more? At one point I was sending data from USB2-connected drive, internal drive and DVD and I was still far from maxing out bandwidth - and the target drive was far from "fast" one.

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