Hello,

SCSI Reservation conflicts are do to performing to many VMFS metadata updates simultaneously. Depending on your SAN/iSCSI server the limit on simultaneous metadata updates is severely limited before you start to through SCSI conflict messages.

First things I would do: Verify the firmware level of your SAN, Fabric Switches, and HBAs are all at the desired level. For example, if you have a Hitachi SAN there was a firmware upgrade required so that the reservations responded much faster and therefore limited the amount of conflicts. Without this minimum version, conflicts would happen constantly.

Second thing I would do, is verify any 3rd party agents, or in house written scripts that run on your ESX hosts on a regular basis. If for example, you constantly 'touch' the files on your SAN to make changes to times, ownership, or groups, and you are doing this simultaneously on ALL your ESX servers, you could easily throw 1000s if not millions of SCSI Reservation conflicts.

Are you touching (file metadata changes), creating, removing, vmotioning, backing up (create and delete) VMs on the same LUN simultaneously? The limit on the number of metadata updates is on a per LUN basis.

I would take your LUN metadata activities and pare them down to only 1 per LUN at any given time and slowly increase that number until you see reservations conflicts. That will give you the upper limit that you can do per LUN.

Best regards,
Edward