Solaris Volume Manager Administration Guide

About RAID-1 Volume Options

The following options are available to optimize mirror performance:

You can define mirror options when you initially create the mirror. You can also change mirror options after a mirror has been set up and is running. For tasks related to changing these options, see How to Change RAID-1 Volume Options.

RAID-1 Volume Read-and-Write Policies

Solaris Volume Manager enables different read-and-write policies to be configured for a RAID-1 volume. Properly set read-and-write policies can improve performance for a given configuration.

Table 10–1 RAID-1 Volume Read Policies

Read Policy 


Round-Robin (Default) 

Attempts to balance the load across the submirrors. All reads are made in a round-robin order (one after another) from all submirrors in a mirror. 


Enables reads to be divided among submirrors on the basis of a logical disk block address. For example, with a two-way submirror, the disk space on the mirror is divided into two equally-sized logical address ranges. Reads from one submirror are restricted to one half of the logical range. Reads from the other submirror are restricted to the other half. The geometric read policy effectively reduces the seek time that is necessary for reads. The performance gained by this read policy depends on the system I/O load and the access patterns of the applications. 


Directs all reads to the first submirror. This policy should be used only when the device or devices that comprise the first submirror are substantially faster than the devices of the second submirror. 

Table 10–2 RAID-1 Volume Write Policies

Write Policy 


Parallel (Default) 

Performs writes to a mirror that are replicated and dispatched to all of the submirrors simultaneously. 


Performs writes to submirrors serially (that is, the first submirror write completes before the second submirror write is started). This policy specifies that writes to one submirror must be completed before the next submirror write is initiated. This policy is provided in case a submirror becomes unreadable, for example, due to a power failure. 

Pass Number

The pass number, a number in the range 0–9, determines the order in which a particular mirror is resynchronized during a system reboot. The default pass number is 1. The lower pass numbers are resynchronized first. If zero is used, the mirror resynchronization is skipped. A pass number of zero should be used only for mirrors that are mounted as read-only. Mirrors with the same pass number are resynchronized at the same time.