Logical volume strategy

The policies described here help you set a strategy for logical volume use that is oriented toward a combination of availability, performance, and cost that is appropriate for your site.

Availability is the ability to access data even if its associated disk has failed or is inaccessible. The data might remain accessible through copies of the data that are made and maintained on separate disks and adapters during normal system operation. Techniques such as mirroring and the use of hot spare disks can help ensure data availability.

Performance is the average speed at which data is accessed. Policies such as write-verify and mirroring enhance availability but add to the system processing load, and thus degrade performance. Mirroring doubles or triples the size of the logical volume. In general, increasing availability degrades performance. Disk striping can increase performance. Disk striping is allowed with mirroring. You can detect and remedy hot-spot problems that occur when some of the logical partitions on your disk have so much disk I/O that your system performance noticeably suffers.

By controlling the allocation of data on the disk and between disks, you can tune the storage system for the highest possible performance. See Performance management for detailed information on how to maximize storage-system performance.

Use the following sections to evaluate the trade-offs among performance, availability, and cost. Remember that increased availability often decreases performance, and vice versa. Mirroring may increase performance, however, the LVM chooses the copy on the least busy disk for Reads.

Note: Mirroring does not protect against the loss of individual files that are accidentally deleted or lost because of software problems. These files can only be restored from conventional tape or disk backups.