I don't know if it's anything like this still today, but ideally for RAID setups to work well the drives should be as close in spec as possible (ideally, the same drives). Mixing drives too far mismatched leaves it up to the controller to keep drives coordinated.
When we did RAID 1 for a setup at work (lol budget constraints but we needed something for storage) IT insisted that we at least had a proper hardware RAID card. I can't remember whether the rebuilds were fast, or if they ran online and just slowed us down for a bit, but we were never down restoring for more than a couple hours.
The irony of the situation was that we actually were blowing ALL the hard drives more frequently in that box. At first we thought it was just the power supply (Oh, that day was terrible. PS blew up alongside one drive, and when we replaced drive+PS the tech may have picked the wrong direction to restore :X)
But, as it turned out the case just was too dang hot to run 2 5400 and 2 7200RPM hard drives at once. (Yes, it had enough bays to fit it all.) Even after beefing up the power supply we would have to replace a drive every 9-12 months, and usually they were in the same location on the case.
FWIW it was an i7-920 with 12GB ram, nice SI Raid Card, running Server 2008 Terminal server. (Just... don't ask.)