From the SQL Server books on line about raid levels

Level 1

This level is also known as disk mirroring because of its use of a disk file system called a mirror set. Disk mirroring provides a redundant, identical copy of a selected disk. All data written to the primary disk is written to the mirror disk. RAID 1 provides fault tolerance and generally improves read performance (but may degrade write performance).

Doesn't seem to me that improved read performance is as desirable as write performance of the transaction logs?