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Perspectives
April 10, 2015
Oracle VM Server for SPARC 3.2 - Enhanced Virtual Disk Multipathing
Multipath groups are arranged in an active/standby pair of connections to the same physical media. In case of a path or service domain failure, I/O activity continues on a surviving path. This is also helpful for rolling upgrades: a service domain can be rebooted for an upgrade, and virtual disk I/O continues without interruption. That's important for continuous availability while upgrading system software.
A previous limitation was that you could not determine by commands which path was active, and you couldn't force activity onto a selected path. That meant that all the I/O for multiple virtual disks went (typically) to the primary path instead of being load balanced across service domains and HBAs. You could deduce which service domains were actively doing disk I/O by using commands like iostat, but there was no visibility, and no way to spread the load.
Oracle VM Server for SPARC addresses this by adding command output that shows which path is active, and let you switch the active path to one of the available paths. Now, the command 'ldm list-bindings' shows which path is active, and the command 'ldm set-vdisk' lets you set which path is active.
For further details and syntax, please see the documentation at Configuring Virtual Disk Multipathing
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Unfortunately only works fully with domains running at least Solaris 11.2.1.0.0 (SRU 1). For Solaris 10 domains the list-bindings command shows the multipath disk state as unknown and the 'set-vdisk volume=' command only changes the path for the next reboot. :( Any chance of it being fully supported for Solaris 10 domains in a future update?