Disk devices can be exported by the Virtual I/O Server. This topic gives information about what types of disks and configurations are supported.
The virtual SCSI (VSCSI) Client Adapter Path Timeout feature allows the client adapter to detect whether a Virtual I/O Server is not responding to I/O requests. Use this feature only in configurations in which devices are available to a client logical partition from multiple Virtual I/O Servers. These configurations could be either configurations where Multipath I/O (MPIO) is being used or where a volume group is being mirrored by devices on multiple Virtual I/O Servers.
If no I/O requests issued to the VSCSI server adapter have been serviced within the number of seconds specified by the VSCSI path timeout value, one more attempt is made to contact the VSCSI server adapter, waiting up to 60 seconds for a response.
If, after 60 seconds, there is still no response from the server adapter, all outstanding I/O requests to that adapter are failed and an error is written to the client logical partition error log. If MPIO is being used, the MPIO Path Control Module will retry the I/O requests down another path. Otherwise, the failed requests will be returned to the applications. If the devices on this adapter are part of a mirrored volume group, those devices will be marked as missing and the Logical Volume Manager logs errors in the client logical partition error log. If one of the failed devices is the root volume group (rootvg) for the logical partition, and the rootvg is not available via another path or is not being mirrored on another Virtual I/O Server, the client logical partition is likely to shut down. The VSCSI client adapter attempts to reestablish communication with the Virtual I/O Server and logs a message in the system error log when it is able to do so. Mirrored volume groups must be manually resynchronized by running the varyonvg command when the missing devices are once again available.
A configurable VSCSI client adapter ODM attribute, vscsi_path_to, is provided. This attribute is used to both indicate if the feature is enabled and to store the value of the path timeout if the feature is enabled.
The system administrator sets the ODM attribute to 0 to disable the feature, or to the time, in seconds, to wait before checking if the path to the server adapter has failed. If the feature is enabled, a minimum setting of 30 seconds is required. If a setting between 0 and 30 seconds is entered, the value will be changed to 30 seconds upon the next adapter reconfiguration or reboot.
This feature is disabled by default, thus the default value of vscsi_path_to is 0. Exercise careful consideration when setting this value, keeping in mind that when the VSCSI server adapter is servicing the I/O request, the storage device the request is being sent to may be either local to the VIO Server or on a SAN.
The vscsi_path_to client adapter attribute can be set by using the SMIT utility or by using the chdev -P command. The attribute setting can also be viewed by using SMIT or the lsattr command. The setting will not take affect until the adapter is reconfigured or the machine is rebooted.