Raid 1 is mirroring only. For data integrity reasons I can't see how they could read from any but the master mirror.
WAG alert:
Once the two disks are synchronized, it sounds perfectly reasonable to writes to take the same amount of time (since all data has to be written to both drives), but for reads to be significantly faster by reading from both spindles. There really is no "master" in an equal set of two, I think. Both contain identical data, so you should be able to read from both. I think.
By the way, the Promise cards *are* software RAID... all the real RAID computations are done by the driver using the computer's resources. The trick is that the binary driver for Linux is probably less mature and less flexible than Linux native software RAID, so I've always used Promise and HighPoint controllers simply as additional EIDE/ATA controllers and used Linux software RAID. Excellent results. Note that Linux software RAID is also capable of RAID-5, IIRC, which the Promise drivers are not.
If you have the budget, I'd strongly recommend the 3Ware cards. Real hardware RAID, native Linux kernel support since 2.2.x, fast, very reliable, and not expensive.
Cheers,
-- Rodolfo J. Paiz rpaiz@xxxxxxxxxxxxxx http://www.simpaticus.com
