SAS Adapter Performance Boost with VIOS

Resolving The Problem

See the following link that has documentation on the requirements and setup:https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/IBM%20i%20Technology%20Updates/page/SAS%20Adapter%20Performance%20Boost%20with%20VIOS

VIOS Configuration

Creating RAID Arrays

For an IBM i configuration with VIOS, a virtual disk that supports 520-byte sectors can be created only from a physical volume (“hdisk”, in VIOS terminology) that represents a SAS RAID array.  Each eligible hdisk must be created from one or more physical SAS disk devices (“pdisks”) that have been grouped together into a RAID array.  Prior to being added to a RAID array, each pdisk must be formatted to use a RAID block size to make it capable of storing the additional 8 bytes of data per sector needed by the IBM i client partition. Virtual target devices backed by other types of disk storage -- such as logical volumes, logical devices from a shared storage pool, or other physical volume types -- do not support 520-byte sectors.

In the simplest configuration, one physical pdisk may be used to create a RAID 0 array which produces a single hdisk that will then be capable of supporting 520-byte sector I/O.  Multiple pdisks may also be grouped together to produce an hdisk with higher levels of protection, if desired.

A pdisk that is not added to a RAID array, but is instead formatted as a standalone SAS hdisk, will not support the IBM i 520-byte sector format.

See the InfoCenter topic on SAS RAID Controllers for AIX for more information on managing SAS RAID arrays in the VIOS.

Creating Virtual Disks

Once a SAS RAID array hdisk has been created, a virtual disk can be constructed from that device and assigned to a server vhost device using the mkvdev command.  For example, the following command creates a virtual disk named “vtscsi0” from a physical volume named “hdisk0” and attaches the virtual device to virtual adapter “vhost0”:

$ mkvdev –vdev hdisk0 –vadapter vhost

vtscsi0 available

See the InfoCenter topic on VIOS and IVM Commands for more information on the mkvdev command.

Only virtual disk devices created from a RAID array on a supported SAS adapter with the appropriate microcode and software levels will be seen by the IBM i client partition as 520-byte sector capable disk units.  All others will remain 512-byte sector disks.