You can't.  That is not how the PERC's Online Capacity Expansion works.  If you swap them out one at a time like that, the only thing you can do with the new space is create a new (second) RAID 5 array across the disks.  This will show as a separate "disk" to the OS, so it cannot be used to merge with existing partitions. You may read about an operation used to do this - called a retag - but this is a RECOVERY operation and was never intended to be used on an array of a different size (to expand).  Best case scenario, it will appear to work, then crash days, weeks, or months later.  If you don't mind the downtime or recovering from backup when it crashes, then this is a "shortcut". If you must have the space accessible to existing partitions (merging, etc.), then you need to backup, remove small disks, insert large disks, create new/larger RAID 5, restore.  If you are ok having the new space appear to the OS as a new/separate "disk", then swap them out one by one. The way Online Capacity Expansion works, is you can expand an array - while online/live - by ADDING disks to the RAID array.  For example, if you have a 3-disk RAID 5, you can add another disk (or more) and convert the 3-disk RAID 5 to a 4-disk RAID 5 (or however many disks you have/add).
Hello, We have a Power Edge 2900 with raid 5 system. Running low on space and want to change out the 3 73gb drives with one spare to 146gb drives with one spare. I have read that you can do this one drive at a time but how do you add the NEW unused space into the existing virtual disk to be used once all drives come back on line. Current system is windows 2003 sbs sp2 raid 5 on perc 5/I with one virtual drive partitioned into 2 drives C: and D: Thank you in advance,  
PE 2900 raid 5/i