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Queue Depth values and Disk.SchedNumReqOutstanding


I have a question regarding Queue Depth values in vmware ESX:

Lets say that we have 1 ESX server with 2 HBA cards, connected to 4 Target ports (2 paths for each HBA) in a VMAX controller for example to 1 LUN working in a round-robin fashion/ PowerPath/VE.

The QD for each HBA is set to 32 and the Disk.SchedNumReqOutstanding is set 32 as well.

will I be able to get 64 Queues in total (32 for each HBA) or only 32 queues because Disk.SchedNumReqOutstanding is limiting us?

If so wouldn't it be smart to limit each HBA to 16 QD while the Disk.SchedNumReqOutstanding stays at 32?

Thanks in advance,

Ben Raz.

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Re: Queue Depth values and Disk.SchedNumReqOutstanding

Hi Ben,

in your design the Queue Depth for the single LUN would be 4*32.

You could easily verify this using esxtop.

Switch to the disk device view and use the NUM pad (2 or 8) to select the VMAX LUN.

Expand the view using 6 from NUM pad.

This will show you all paths to the selected device and the queue depth of each path.

Starting with ESXi 5.5 the handling of Disk.SchedNumReqOutstanding has changed.

More details could be found here.

Setting the Maximum Outstanding Disk Requests for virtual machines (1268)



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