TSX-EMEA: ESX Storage virtualisation insights

Presenter: Thorbjorn Donbaek (Senior Storage Developer, VMware)

This session was all about tweaking storage settings – especially in the area of analysing VM driver queues, vmkernel disk queues and fibre-channel queues. It was my first session of the day and it was a bit of struggle to keep up. I got the impression it was the speakers first session of the day and some of the finer detail went over my head. Perhaps that says more about my good my storage knowledge is. Anyway, I got some tips and tricks such as: 

  • Some older distros of Linux work better with the BusLogic driver. In general LSIlogic is preferred for Windows
  • There as some useful KB articles which discuss the possible benefits of adjusting queue lengths of Qlogic (KB 1269) and Emulex cards (KB 8535211)
  • The vmkfstools command options of -I are still preferred for moving large files around as it still reduces the SCSI reservations required for disk transactions. Unlike commands like CP which handle file creation less efficiently. 
  • Physical Compatibility RDMs can cause problems in RDMs. This is because the VM places a SCSI reservation on the device (such as a tape device) using the WWN of the original host. When the VM is moved via VMotion, these reservations remain tied

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  • to the original hosts WWN value. RDMs with virtual compatibility remain unaffected. 

Later the preset went on to discuss some issues with VMware iSCSI Software Initiator. Most of this was familiar ground for me. Except for one issue I’d never come across. The NICs used behind a VMkernel port group for iSCSI must be in the same V/LAN – or broadcast domain. This can lead to single point of failure on the physical switch. I’m not sure how much of show stopper this is. Most Cisco configurations I see have the second switch up-linked by a passive connection the primary switch anyway. But perhaps one to watch out for

This was first published in April 2007

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