I have a 16 drive hardware RAID array which has 15/16 3 Gb/S SATA drives. On replacing a failing drive I realized the replacement was a 6 GB/S drive (same brand/cache,size though).
Is this likely to cause issues down the road - if I'd realized beforehand I wouldn't have tried, but the RAID array is rebuilding fine (which is good!).
I just don't want an issue where under high load this causes problems. My guess would be everything ends up being bottlenecked by the lowest speed connection, so the 6 Gb/s SATA will end up acting like a 3 Gb/s SATA anyway.
Edit - specific models:
RAID controller - 3ware 9650SE-16ML RAID Disks Western Digital 500 GB - WD RE WD5003ABYX # 3 Gb/S (15/16 of the drives) Western Digital 500 GB - WD RE WD5003ABYZ # 6 Gb/S (1/16 of the drives)