Raid 1 is a mirror so the computer ought to run fine with 1 disk.
One disk is probably marginal, so during the rebuild, the OS rereading and rewriting until it suceeds.
Try looking at the event viewer to see if any errors or warnings show up to learn which disk is bad.
Power down and disconnect the power and the data cable to 1 disk, reboot.
When booting with one disk good disk, the response should be normal.
The computer performance with the bad disk should be slow.
Backup your data ASAP.
Replace the bad disk with an identical disk, and let it rebuild.
Thank you VERY much for the suggestion and information on systematically testing each drive. You hit the nail on the head. One of the drives had failed and the system was unable to boot from it. The system is performing far better now on just the one functioning drive than it has for quite some time. This leads me to believe the the failed drive was in a state of decline for quite a while. I think it's a shame that the Storage Manager software cannot accurately detect and report the status of a failed member in an array.
Now, the next challenge is going to be finding an identical replacement drive. My current drives are WDC Model WD2500JS and it looks like they are available only from a few suppliers via mail order. But, at least they are available.
Thanks again for taking the time to offer your suggestions. Happy New Year.
Hey. One more thing, do a disk scan.
From the explorer, right click on the drive, select properties, then select all the checks for the file system and disk.
It'll do a scan the next time it boots, be prepared for it to take a long time.
Backup your data before doing this.
If it runs okay, then you can be confident that the OS and the raid are okay.
It's much better to find out now that something is wrong than later.