Comments on: PVSCSI and Low IO Workloads

By: Jesse

Jesse — Wed, 26 Oct 2011 16:07:47 +0000

Bumping an old one here, but this is one of the better discussions out there regarding pvscsi. FYI, I’ve defaulted all my new VMs to pvscsi (mostly 2008 R2 guests on 4.1U1 hosts). Has worked great, but recently we’ve had three bluescreens when growing data disks on-the-fly. VMware’s recommendation (from http://kb.vmware.com/kb/1010398) is that the boot disk should be on a pvscsi controller by itself, and the subsequent data disks should be on at least one other one (SCSI ID’s of 1: or higher).

By: drummonds

drummonds — Fri, 14 Oct 2011 00:02:09 +0000

You can and should always use the PVSCSI driver now. This article was written a year and a half ago. Its content pertains to vSphere 4 with no updates applied. These issues were corrected through updates to vSphere 4 that were also folded into subsequent versions of the product.

By: Richard McLane

Richard McLane — Thu, 13 Oct 2011 22:12:00 +0000

So with the added latency in low IO situations resolved, is it worth using this as a default adapter (for OSes that support it) for the increased CPU efficiency? It’s the default device for RHEL 6 already, but I’m thinking specifically 2008 R2. We’d need to ensure that the driver for this (from the VMware Tools) is loaded into the boot image as well I assume.

By: Tom Miller

Tom Miller — Fri, 25 Feb 2011 15:44:42 +0000

Thanks Scott for the fast response. I’ll make sure to share this with the client.

By: drummonds

drummonds — Thu, 24 Feb 2011 03:51:03 +0000

I spent some time digging into the benefits of distributing VMDKs across multiple virtual HBAs. VMware never quantified any gains from this practice but we all agreed that there should be some value. Most likely the gains would come from an increased queue in the guest. But to realize these gains you would have to be distributing the VMDKs across multiple VMFS volumes, too. And to measure a difference you would have to be driving a large number of IOs. Certainly about 50K IOPS.

By: Tom Miller

Tom Miller — Wed, 23 Feb 2011 15:44:03 +0000

Scott,
Great work as always. So it’s pretty obvious to use pvscsi with high I/O workload. Our client is planning on running SLES11 sp1 with Oracle 11G. He is planning on using one disk for boot and “/” and two more disk using Oracle ASM for load balancing within Oracle across both data disk. He ask a good question. When adding the third disk should it be added to a separate controller from the second disk. Would this have any performance gains or is this over complicating this with nominal benefits?

By: How to use the pvscsi driver on Ubuntu LucidTork Wrench | Tork Wrench

How to use the pvscsi driver on Ubuntu LucidTork Wrench | Tork Wrench — Mon, 07 Feb 2011 05:31:12 +0000

[...] first it’s not supported by VMware on the boot disk as described above, and secondly it should not be used in a low throughput environment. This entry was posted in howto and tagged 10.04, lucid, pvscsi, ubuntu. Bookmark the permalink. [...]

By: Irfan

Irfan — Fri, 31 Dec 2010 00:37:03 +0000

Careful there. There are plenty of “performance-sensitive” apps out there which are latency bound. In those situations, it is critical to have a technique that is adaptive. Of course, in vSphere 4.1, we fixed this issue and made the pvscsi interrupt coalescing algorithm to match the version we originally implemented in our virtualized LSI controller so this particular issue should be behind us now. For those curious, the actual technique is super cool and we published a very approachable paper on said topic. Search for virtual interrupt coalescing under my name on Google.

By: More vSphere 4.1 Enhancements – Welcome Back PVSCSI Driver! « thelowercasew.com

Mon, 16 Aug 2010 13:08:07 +0000

[...] In a post on his vPivot blog, former VMware performance guru Scott Drummonds echoed the sentiments and stated that this issue would be resolved in a future release of vSphere. He noted that the PVSCSI driver was only slightly slower than the LSI driver in certain scenarios but acknowledged that it could result in slightly less performance with no efficiency gains. [...]

By: drummonds

drummonds — Fri, 23 Jul 2010 05:48:47 +0000

PVSCSI coalescing has been fixed in ESX 4.1. VMware has checked in the fix to the code branch that will produce ESX 4.0 U3. I am not the right person to comment on PVSCI support for SCSI3.