Configuring disks to use VMware Paravirtual SCSI (PVSCSI) adapters

March 25th, 2010 by jason Leave a reply »

This is one of those “I’m documenting it for my own purposes” articles.  Yes I read my own blog once in a while to find information on past topics.  Here I’m basically copying a VMware KB article but I’ll provide a brief introduction.

So your wondering if you should use VMware Paravirtual SCSI?  I’ve gotten this question a few times.  PVSCSI is one of those technologies where “should I implement it” could be best answered with the infamous consulting reply “it depends”.  One person asked if it would be good to use as a default configuration for all VMs.  One notion that I would agree on by and large is that I feel the support complexity increases when using PVSCSI and it should only be used as needed for VMs which need an additional bit of performance squeezed from the disk subsystem.  This is not a technology I would implement by default on all VMs.  Dissecting the practical beneifts and ROI of implementing PVSCSI should be performed, but before that, your valuable time may be better spent finding out if your environment will support it to begin with.  Have a look at VMware KB Article 1010398 which is where the following information comes from, verbatim.

It’s important to identify the guest VMs which support PVSCSI:

Paravirtual SCSI adapters are supported on the following guest operating systems:

  • Windows Server 2008
  • Windows Server 2003
  • Red Hat Enterprise Linux (RHEL) 5

It’s important to further identify more ambiguous type situations where PVSCSI may or may not not fit:

Paravirtual SCSI adapters also have the following limitations:

  • Hot add or hot remove requires a bus rescan from within the guest.
  • Disks with snapshots might not experience performance gains when used on Paravirtual SCSI adapters or if memory on the ESX host is overcommitted.
  • If you upgrade from RHEL 5 to an unsupported kernel, you might not be able to access data on the virtual machine’s PVSCSI disks. You can runvmware-config-tools.pl with the kernel-version parameter to regain access.
  • Because the default type of newly hot-added SCSI adapter depends on the type of primary (boot) SCSI controller, hot-adding a PVSCSI adapter is not supported.
  • Booting a Linux guest from a disk attached to a PVSCSI adapter is not supported. A disk attached using PVSCSI can be used as a data drive, not a system or boot drive. Booting a Microsoft Windows guest from a disk attached to a PVSCSI adapter is not supported in versions of ESX prior to ESX 4.0 Update 1

For more information on PVSCSI, including installation steps, see VMware KB Article 1010398.  One more important thing to note is that in some operating system types, to install PVSCSI, you need to create a virtual machine with the LSI controller, install VMware Tools, then change to the drives to paravirtualized mode.

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