I have IBM eServer with ServeRaid-7K on board controller and have 3 SCSI 73GB hard drives configured in RAID-5 array. Hard Drives are running critically low on space and I bought 3 300GB scsi Ultra320 hard drives to upgrade the existing 73GB HDs. What's the best possible way to upgrade these hard drives without a chance of loosing data or needing to reinstall everything? Please help !!

First, buy an external storage device, at least 80GB (although it's currently difficult to find any _smaller_ size!) and make a file-by-file, folder-by-folder, backup of your 73GB of "data".

Second, buy another external storage device, and do a Google-search for "drive image freeware".
Pick one of those applications, and do a "image" backup to this second external storage device.

Third, disconnect the 3 "old" drives, carefully label them, and set them aside.

Fourth, connect the 3 "new" drives, delete the old RAID-5 array definition,
and create a new RAID-5 array definition.

Fifth, do an "image restore" from the second external storage device to the new array.

If you have any problems, all you need to do to "back-out" is to:
* disconnect the "new" drives
* reconnect the "old" drives
* delete the "new" array definition
* redefine the "old" array definition

and you're back to the "old" configuration.