"PVSCSI adapters are not suited for DAS environments" ??

[nbarsotti]

There is a vmware knowledge base article ( ) that says "PVSCSI adpaters are not suited for DAS environments." Can someone please shed some light on why this is? I am running 1 VM on local storage with a second PCSCSI adapter and I have not noticed any problems. Please help.

[jasonlitka]

According to this document it was designed for iSCSI and FC datastores. My guess is that it has something to do with how I/O's are queued on those type of storage systems.

Jason Litka

[Texiwill]

Hello,

It is not quite possible to create an RDM on a local disk, not can you do so on NFS. PVSCSI comes into play when you use RDM or similar disk types more than when using a VMDK. So iSCSI/FC are the best options for non-VMDK type disks as they present a LUN.

Best regards, Edward L. Haletky VMware Communities User Moderator, VMware vExpert 2009
Now Available on Rough-Cuts: 'VMware vSphere(TM) and Virtual Infrastructure Security: Securing ESX and the Virtual Environment'[/url]
Also available 'VMWare ESX Server in the Enterprise'[/url]
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[nbarsotti]

Hello Texiwill,

Thank you for the reply. So are you saying that there is no real benefit from using PVSCSI adapter when the back end is a VMDK file, no matter where the VMDK files is store (NFS, iSCSI, or Fiber)? Are you saying PVSCSI only makes a difference if you user a RDM? If that is the case then PVSCSI seems pretty useless for most people since most VM's use VMDKs. With that said will the PVSCSI adapter hurt perfromance when used on a DAS array and associated VMDK file? Thank you in advance.

[tbsky]

hi:

my real scsi card is lsi ulrta320. i trid to use pvscsi with linux. and i found thare are no difference in speed/cpu utilitization compare with lsi parallel driver.

i don't know the situation on windows. but i guess it's the same. so vmware maybe right. it's not worth to use pvscsi in DAS system.

[Texiwill]

Hello,

The PVSCSI driver will work on all types of disks but you may not get any benefit from VMDKs on DAS from a performance perspective. THe PV driver will know about the virtualization layer and help with what is going on there in some cases but not all. You will have to run some tests with your workloads. Just because there is a paravirtualized driver does not mean you will actually get a performance improvement. In some cases yes, in others not at all.

Best regards,

Edward L. Haletky VMware Communities User Moderator, VMware vExpert 2009, Virtualization Practice Analyst[/url]
Now Available: 'VMware vSphere(TM) and Virtual Infrastructure Security: Securing the Virtual Environment'[/url]
Also available 'VMWare ESX Server in the Enterprise'[/url]
[url=http://www.astroarch.com/wiki/index.php/Blog_Roll]SearchVMware Pro[/url]|Blue Gears[/url]|Top Virtualization Security Links[/url]|Virtualization Security Round Table Podcast[/url]

[nbarsotti]

Thanks for the input. PVSCSI has been working just fine on my DAS vmdk.