We have a 6 HDD RAID 5, divided in 2 partitions, C and D, where C holds OS, D holds Exchange Data. 3 of the HDDs are 32GB 3 are 16GB. We want to do the following. Purchase same 3x HDDs size 32GB. Replace them one after another (i.e. replace 1, let raid rebuild, replace 2, let raid rebuild, and so on) to get all 6 drives have extra 16GB. Ultimately we want to use that extra 16GB on each drive to create a new RAID 5, in addition to the current one, lets say drive letter E:. Is this possible and are there any pitfalls along the way! Thank you !

I have to assume you are doing hardware raid presently. From my experience you don't have an option to use the 16gig leftover space via hardware controller. It is all or nothing. You could do a software raid array. But then you are mixing hardware and software raid access to the drives. This can lead to problems. I would also point out, though this is a factory standard raid setup, it limits growth and recovery. You would be much better off with an expandable solution. This would involve cloning c: and d: as separate images. You would configure two 32 gig drives as a mirror and restore the c: image to the mirror. You would configure three 32gig drives as raid5 and restore the d: image to the raid array. You would have the last drive as a hot spare to failover if a drive died in either raid array. Down the road if you wanted to expand the raid5 you can backup/image, init the new array with added space, format in Disk Management and then restore. Beauty of this is you don't have to mess with the OS drive. If you want to expand the mirror you break the mirror, put a larger drive in, image from the small drive to the larger, replace the small drive with a larger and then mirror. You never touched the data drive.

Normal answer starts with create backup and test it. Loss of data, damage to delicate parts, short out, drop, spill coffee (oh, I never did that). You need to play with the raid array software/firmware and know the owner manual before you play with this. "Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10

To Wanderer: Thank you for the guidance Wanderer. 2 things that i find we may have problem with in this suggestion is 1. We need the extra space for the data partition rather than the OS drive, and may need to utilize all 4 drives. Even with all 4 Drives we'll get somewhat less free space. Also this server has only 6 slots so we cannot add additional drives. What we have is what we can work with. The second problem would come from the fact we do not have additional drives to play with, i.e. we have only 3 new HDDs x 32GB each and i dont' see how we can test backup/restore without at some point relying solely on the backup until we restore to the new configuration (provided we do Raid 1 + 5). This also involves additional downtime that the company this is done may not be able to afford. The original request was intended to minimize the downtime (to virtually 0) and accomplishing the same task. Another problem is that the 3x 32GBs are already purchased, and we don't have the option to return and get larger HDDs (to accommodate same expansion with fewer drives for RAID 5, if we set aside 2x 32GB for the OS drive). Is there a scenario that can accommodate all of the above constraints that can work with both minimum down time (ideally 0) and with the hardware that is already available?

To Jefro: Hey Jefro, thank you also for your reply. With this scenario, we unfortunately have limited ability to play with the software/hardware, being this is exchange server that needs to be live 24/7.Covering the raid sofrware (both hardware/software) goes without saying, however I am looking for best practices given our scenario in order to both accomplish the task, gain the necessary additional disk space and at the same time keep the server running. I know this maybe asking for a lot, but unfortunately we cannot afford to skip on any of the requirements :-)

Your only option would be to do a software raid on top of your hardware raid. It just isn't something I would do with a production server. See why raid5 and partitions are such a bad idea? This factory config causes all sorts of problems like yours. Can Disk Management see the available space now on the 32gig disks? Some raid controllers I have worked with do not report the space to the OS.

Hey Wanderer, I will be working to get the new hard drives installed this week probably and will let you know how it goes. My hopes are it will see the free space and i'll be able to set it up as a new drive letter. Otherwise I'll have to work on getting management understand why i need to re-configure the server to match your solution, approve the downtime and work on deploying from backups.. i'll keep you posted! Thank you again for helping with this!