TSX-EMEA: Top support issues I

Describes the dangers of using Fixed-Preferred policies against an Active/Passive SAN array. Basically, if you do this you will find the 3-conditions checked by ESX to detect a failure are reduced to just one.

Presenter: Cormac Hogan

I know Cormac from the forums where he has helped me, especially in the command-line guide I wrote earlier last year. He did not disappoint us. Cormac very simply explained the “Path Thrashing” issue that can affect active/passive arrays that have been incorrectly configured. Additionally, he outlined the scenarios associated with “VMFS Resignaturing” which affects ESX hosts that have both the original LUN and the snapshot LUN presented to them at the same time. I know about these issues already, but Cormac certainly did give me the pen-drop-moment. He also pointed out the dangers of using fixed-preferred policies against an Active/Passive SAN Array. Basically, if you do this you will find the 3 conditions checked by ESX to detect a failure are reduced to just one. So, while it will work, it’s not in best interests.

Lastly, Cormac outlined the diskpart command used on a VCB proxy, (automount disable and automount scrub) which will stop a VCB proxy from assigning driveletter and signatures to the VMFS volumes it has access to.

This was first published in April 2007

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