Mavericks RAID 1 unreliable?

Question

Short version: RAID 1 array rebuild is failing with one drive working in the set, but failing after an hour or two (variable) attempting to rebuild to another drive. I've changed drive and drive bay and the rebuild still fails. The apparently working remaining source drive from the failed mirror seems to be OK as Time Machine completed a full backup of its contents without issue. Nothing is logged in Console. Debug suggestions welcomed.
Long version: I've been overseas for a while with my Mac laptop, while my Mac Pro sat back home gathering dust for a few months, running a fairly early 10.8 version. When I got back, I upgraded it to 10.8.5, then retail Mavericks via the App Store.
The machine is a 2008 Mac Pro 3.1 with all four internal drive bays populated. The four drives are configured as two volumes, both RAID 1 (mirrored) for fault tolerance. Time Machine runs over both drives to an external enclosure. The external enclosure itself was reporting failures on one drive in the Time Machine striped array. Being quite old, I replaced all drives in the striped array and ran a complete backup of the RAID 1 volumes in the Mac Pro. This completed successfully, so all files on both volumes are clearly readable without error. Normal incremental backups since then have proceeded without issue.
It was setting up the replacement Time Machine drives in Disk Utility under Mavericks where I first saw that one of the two internal hard drive RAID 1 volumes, the boot volume, was marked as "degraded". The drive in Bay 3 was marked as "Failed". I tried a rebuild, and it seemed OK for a while, but then dropped back to "Failed". Another rebuild attempt failed part way through.
So, assuming another hard drive fault, I bought another two drives to replace the two internal discs making up the boot volume RAID 1 array. Replacing the drive in Bay 3, I tried to rebuild - but - same problem. It failed after about an hour or two of rebuild. Nothing at all is logged in Console at the point of failure - plenty of messages when the array is being set up and rebuild starts, but oddly, no messages at all when it fails. Disk Utility just says "Failed" and the rebuild halts.
I've now swapped the drives in the two bays, to see if the actual drive bay 3 in the Mac Pro was faulty. The machine was now booting from the only working original drive in the set, from Bay 3. It's working fine from there as I type. However, a rebuild to the new drive, now in Bay 4, failed in the same way as usual. Faulty new drive perhaps? So now I swapped the one new drive for the other one I'd bought at the same time. Rebuild - same result. Failed.
Even if I swap drive bays and with three different hard discs, I cannot rebuild the RAID 1 array for the boot volume. The other RAID 1 volume in the machine seems to be fine, though the machine doesn't boot from it and its overall data traffic levels are lower. But since Time Machine can read all files on both volumes apparently with no trouble, it would seem that the one working drive in the RAID 1 boot volume isn't to blame for the rebuild failures (but I might be wrong as the I/O patterns are of course quite different).
I've now no idea how to proceed. Both bay 3 and bay 4 seem to work equally well with the one remaining working boot drive present; meanwhile, neither bay works when attemping to rebuild to either a new or an old hard drive. This looks more and more like a (severe!) Mavericks bug, except the other RAID 1 volume is just fine so far and Google doesn't show any particular complaints about Mavericks and RAID 1 arrangements.
Given the lack of Console information, anyone have any suggestions about how I can find out what the cause of the failure is?

Answer 1

There were no responses, but for the sake of archives and searches: I did not resolve the RAID rebuild issue so took a different approach.
I put the two new drives into bays 1 and 2, booting off the one working boot drive from the original RAID mirrored pair that I'd put in bay 4. I used Disk Utility to configure the new drives as a new RAID mirrored pair with the same volume name as the boot volume, then did a file-level copy of the contents using Carbon Copy Cloner. I then swapped out the old boot drive, put back in my other mirrored pair of general data disks so all four bays were once again populated and started up. So far, the machine has been running fine with no RAID failures noted on the boot or data volumes.
Since the only thing that made a difference to the ability to copy the failing volume's data was the method through which the files were copied, it's hard to escape the conclusion that Mavericks' RAID 1 rebuild code is broken and anyone using software RAID under OS X 10.9 should proceed with extreme caution - and up to date backups!
(So for me the upgrade cost of Mavericks has been the unnecessary purchase of two 2TB hard drives, since it looks like a software fault in the array rebuild, not any kind of disk error in the original drives - but who knows - nothing's logged to console - what a mess).