Requirements for mirroring or striping
Determine whether the data that is stored in the logical volume is valuable enough to warrant the processing and disk-space costs of mirroring. If you have a large sequential-access file system that is performance-sensitive, you may want to consider disk striping.
Performance and mirroring are not always opposed. If the different instances (copies) of the logical partitions are on different physical volumes, preferably attached to different adapters, the LVM can improve Read performance by reading the copy on the least busy disk. Write performance, unless disks are attached to different adapters, always cost the same because you must update all copies. It is only necessary to read one copy for a Read operation.
AIX LVM supports the following RAID options:
| Item | Description |
|---|---|
| RAID 0 | Striping |
| RAID 1 | Mirroring |
| RAID 10 or 0+1 | Mirroring and striping |
While mirroring improves storage system availability, it is not intended as a substitute for conventional tape backup arrangements.
You can mirror the rootvg, but if you do, create a separate dump logical volume. Dumping to a mirrored logical volume can result in an inconsistent dump. Also, because the default dump device is the primary paging logical volume, create a separate dump logical volume if you mirror your paging logical volumes.
Normally, whenever data on a logical partition is updated, all the physical partitions containing that logical partition are automatically updated. However, physical partitions can become stale (no longer containing the most current data) because of system malfunctions or because the physical volume was unavailable at the time of an update. The LVM can refresh stale partitions to a consistent state by copying the current data from an up-to-date physical partition to the stale partition. This process is called mirror synchronization. The refresh can take place when the system is restarted, when the physical volume comes back online, or when you issue the syncvg command.
Any change that affects the physical partition makeup of a boot logical volume requires that you run the bosboot command after that change. This means that actions such as changing the mirroring of a boot logical volume require a bosboot.