Pass Number

A pass number in the range 0-9 can be assigned to a mirror. The pass (resync) number determines the order in which that mirror is resynced during a system reboot. The default is 1. Smaller pass numbers are resynced first. If 0, the resync is skipped. A 0 should be used only for mirrors that are mounted as read-only. If different mirrors have the same pass number, they are resynced concurrently.

Read Policy 

The three read options for mirrors are roundrobin, geometric, and first. The default is roundrobin, also called balanced load. 

roundrobin: All reads are made in a round robin order from all the submirrors in the mirrors. That is, the first read comes from the first submirror, the next read comes from the second submirror, and so forth. 

geometric: Provides faster performance on sequential reads or when you are using disks with track buffering. Geometric reads enable read operations to be divided among submirrors on the basis of a logical disk block address. For instance, with a three-way mirror the disk space on the mirror is divided into three (equally sized) logical address ranges. Reads from the three regions are then performed by separate submirrors (for example, reads to the first region are performed by the first submirror). 

first: Specifies reading from only the first submirror. Use only if you have a second submirror that has poor I/O characteristics. 

Write Policy 

A submirror can be set for parallel or serial writes. The default is parallel; writes are dispatched to all submirrors simultaneously. The serial option specifies that writes to one submirror must complete before the next submirror write is initiated. The serial option is provided in case a submirror becomes unreadable, for example, due to a power failure.