Performance Guidelines

VxVM allows you to optimize data storage performance using the following two strategies:

• Balance the I/O load among the available disk drives.
• Use striping and mirroring to increase I/O bandwidth to the most frequently accessed data.

VxVM also provides data redundancy (through mirroring and RAID-5) that allows continuous access to data in the event of disk failure.

Data Assignment

When deciding where to locate file systems, you, as a system administrator, typically attempt to balance I/O load among the available disk drives. The effectiveness of this approach is limited by the difficulty of anticipating future usage patterns, as well as the inability to split file systems across the drives. For example, if a single file system receives the most disk accesses, moving the file system to another drive also moves the bottleneck to that drive.

VxVM can split volumes across multiple drives. This permits you a finer level of granularity when locating data. After measuring actual access patterns, you can adjust your previous decisions on the placement of file systems. You can reconfigure volumes online without adversely impacting their availability.

Striping

Striping improves access performance by cutting data into slices and storing it on multiple devices that can be accessed in parallel. Striped plexes improve access performance for both read and write operations.

Having identified the most heavily accessed volumes (containing file systems or databases), you can increase access bandwidth to this data by striping it across portions of multiple disks.

The figure, Use of Striping for Optimal Data Access, shows an example of a single volume (HotVol) that has been identified as a data-access bottleneck. This volume is striped across four disks, leaving the remaining space on these disks free for use by less-heavily used volumes.

Use of Striping for Optimal Data Access

Click the thumbnail above to view full-sized image.

Mirroring

Mirroring stores multiple copies of data on a system. When properly applied, mirroring provides continuous availability of data and protection against data loss due to physical media failure. Mirroring improves the chance of data recovery in the event of a system crash or the failure of a disk or other hardware.

In some cases, you can also use mirroring to improve I/O performance. Unlike striping, the performance gain depends on the ratio of reads to writes in the disk accesses. If the system workload is primarily write-intensive (for example, greater than 30 percent writes), mirroring can result in reduced performance.