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Do Hyper-V IDE and SCSI devices both offer equally fast I/O performance when integration services are installed in the guest operating system?

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up vote 7 down vote accepted

According to Microsoft

Although the I/O performance of physical SCSI and IDE devices can differ significantly, this is not true for the virtualized SCSI and IDE devices in Hyper-V. Hyper-V. IDE and SCSI devices both offer equally fast I/O performance when integration services are installed in the guest operating system.

Source

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How can that technically be given that IDE drives per API do only allow one outstanding operation at the same time, while SCSI allows more? –  TomTom Dec 3 '12 at 17:54
    
Oh no!, I attached two Disks (IDE and SCSI) for every VM I created so far. and now you mean it was a wast of time? I had Linux Integration Services installed on all of them. –  Steve Dec 3 '12 at 17:54
    
@TomTom I don't know, Hyper-V isn't my bread and butter, but the source link is directly from TechNet. –  MDMarra Dec 3 '12 at 17:55
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My assumption here is that Microsoft is trying to say "the virtual drives are effectively limited by the underlying storage". Also note the caveat "when integration services are installed in the guest operating system", which leads me to believe that Microsoft is supplying some additional magic with the integration services package. Bottom line: As with all performance claims, test it yourself - manufacturers/vendors lie like dogs. –  voretaq7 Dec 3 '12 at 18:02
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The "SCSI adapter" doesn't actually speak SCSI. It speaks MS Storage Filter API only. The IDE device actually speaks both IDE and the API; once a machine had loaded the drivers necessary for the APIs to function both storage mechanisms work exactly the same. The "IDE Adapter" can't hot-swap drives like the "SCSI" one because of the legacy IDE requirements. They added both types of storage controllers so you could choose your trade-off: Bootable or Hot-Swappable. –  Chris S Dec 3 '12 at 18:09

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