I have a 5 disk (each 72 GB) configured as RAID 5, one of the disk has degraded and requires replacement. Can I introduce a 128 GB disk, will it work? Thanks in advance....KK

Depends...are you referring to a software RAID defined in Windows? If so, the answer is yes. Once you bring the new disk in, you can only use the portion of the disk that you defined in your array (72 out of 128 GB). If this is an array hosted by a hardware RAID card, most likely as well, but you'll need to check the documenation provided by the vendor. Visit: anITKB.com, an IT Knowledge Base.