System information

Advanced Functions
5-1
Chapter 5: Advanced Functions
5.1 Multi-Path IO Solutions
5.1.1 Overview
Multi-path IO allows a host computer to access a RAID system over multiple paths for enhancing system availability and
performance. The RAID system supports multi-path IO either with the bundled proprietary software or by the native multi-
path IO software of the operating systems.
The following RAID systems support multi-path IO solutions:
• 4Gb/s FC-SAS/SATA RAID system
• 3Gb/s SAS-SAS/SATA RAID system
The single-controller systems support the following operating systems:
• Windows 2003 Server 32-bit/64-bit OS (PathGuard )
• Linux with 2.6.x series kernel, like SLES 9/10, RHAS 4/5, RHEL 4/5 (Device Mapper multi-path driver).
• Solaris 10 OS (MpxIO, Multiplexed I/O)
• MAC OS X (default driver)
• VMWare ESX (default driver)
The dual-controller systems support the following operating systems:
• Windows 2003 Server 32-bit/64-bit OS (PathGuard )
• Linux with 2.6.x series kernel, like SLES 9/10, RHAS 4/5, RHEL 4/5 (Device Mapper and proprietary multi-path driver).
For the updated interoperability list and the bundled multi-path software, please contact your supplier.
5.1.2 Benefits
Below are the summarized benefits of the multi-path IO solution:
• Higher availability
With redundant paths, the failure of single path will not result in corruption of the whole system, and the applications
can continue to access the storage devices without being aware of the path failures. This highly enhances the
availability of the whole system.
• Higher performance
The performance of single logical device will not be limited to the upper bound of bandwidth provided by single path,
and it is improved by aggregating the bandwidth of multiple paths. It also outperforms host-side software RAID0
because RAID0 forces I/O to be truncated into data stripes, resulting in overhead and limited size of per-transaction
data transfer.
• Higher bandwidth utilization
With statically assigning paths to logical devices on a controller, the bandwidth of all connections cannot be fully utilized
if the loading on different logical devices is uneven. By transferring data over all paths, bandwidth utilization is more
efficient, and ROI is improved.
• Easier management
With dynamic load balancing, the users need not to worry about either bandwidth planning during the installation or the
reconfiguration for performance tuning. When there is new HBA or new connection is added, the bandwidth created
can be utilized easily. Therefore, MPIO largely reduces the management efforts and the TCO (Total Cost of
Ownership).
5.1.3 Configuring MPIO Hosts and RAID Controller
A path is defined as the link from host to a virtual disk presented by the RAID controller, and it includes the HBA, cables,
and optionally a storage switch. To build multiple I/O paths, there have to be multiple links between the host computer
and the RAID system, and the virtual disks in the RAID system have to be exported to multiple host-interface ports. The
multi-path software on the host computer can access the virtual disks through any of the exported LUNs over the links.
Because multiple HBAs (or multiple ports on single HBA) on a host computer are required to access the same set of LUN
mappings, grouping these HBAs into a host group and using symmetric storage presentation for exporting LUNs would it
ease your configuration tasks.