How to add more space to a RAID 5 array??


Aug 23, 2011
Here is the scenario. We have a server in a small office that is partitioned into 2 hard drives--C: and D and we are basically running out of space. The server has a RAID 5 array with 3 hard drives that are all the same. They are of this type:

Seagate SCSI ST373207LC Revision D703 - 73 Gb.

This is the RAID controller installed:

Primary Controller DELL PERC4/SC, 1 Internal Channel P4SCI

The server is a Dell Poweredge 1800 that was installed a long time ago (2005 - it has Windows 2003 Server running). The people who installed it are no longer in business and every other ‘tech’ place I call basically says to get a new server—that’s not an option because this one is working fine. All I really need is to increase the size of the RAID array. I think that because the server is so old, most tech places feel it’s not really worth their trouble to help me. I have a lot of experience with Windows XP systems, but not a lot with servers, although I know a little. I should also mention that we have Paragon Partition Manager for Servers installed. It was used successfully in the past to reallocate free space between the C: and D drives.

So, here is my plan.

1. I have purchased 2 hard drives of the exact same type the server has. The server has capacity for 6 hard drives,
but now only 3 are being used.
2. Perform a full backup of the server.
3. Insert the 2 new drives into two empty bays.
4. Run Dell OpenManage Server Administrator.
5. Perform a ‘rescan’ of the server and hope it ‘sees’ the 2 new hard drives.
6. Perform a ‘reconfigure’ of the RAID virtual disk.

I am hoping that the above steps will result in larger RAID array. I don’t care how the extra free space is allocated as long as the server recognizes and reconfigures the drives. It would be preferable if all the free space went to the D drive, but if not, then I can use the Paragon program to ‘Reallocate’ the free space.

Are the steps that I outlined above feasible? Am I missing something critical. I have read something about hitting ‘CTRL-M’ during startup and doing something there, but I am not sure what that means. The Dell OpenManage program is much easier to use—I just hope it works.

Any advice would be much appreciated. :hello: :hello:


It's a good thing that you included a full backup.

Adding two new drives will require that you build a new RAID array with five drives. This will cause whatever is on the three existing drives to be erased. In RAID5 with three drives, when you write four "units" of data (size of unit depends on your stripe size) it writes two units plus parity, then two more units plus parity. You can't just add blank space; the data would have to be re-organized across all five disks as four units plus parity.

So your choices are
1) Make a complete copy of everything on your array to external storage. Then do it again to additional external storage, and take that copy home as an off-site backup. Rebuild your RAID with five drives and restore your backup.

2) There is a rare ability to add drives to a RAID5 set. It requires that you not use the system while two-stripe data plus parity is being converted to four-stripe data plus parity; all of the parity has to be recomputed. I have no idea if your system can do it. And, for a production system, I wouldn't consider it to be worth the risk.

3) Hey, buy the new server. Use current enterprise-grade SAS drives.

4) Buy _three_ new hard drives. Build another RAID array. Move drive D to it, and leave all the space on the old array for C.

PS - here's a decent, if old, discussion: . Microsoft TechNet disagrees: , but that's an old article.
As with striped volumes, you cannot add disks to a RAID-5 volume if you need to increase the size of the volume later.
And here's someone who had success:


May 9, 2008
Alternatively, throw out RAID entirely and just use a single high-performance SSD. Sounds like 150GB is too little for you - but you can get fairly cheap (for this kind of business use anyhow) consumer drives up to 600GB.

Since performance is probably going to be way better this route anyhow, I'd opt for something conservative & reliable, e.g. the intel x25-m g3 600GB.


May 14, 2015

A RAID 5 system is better than any single drive, SSD or not. Do you even know what a RAID 5 system is


May 21, 2015

Thanks for your very productive contribution to the discussion tecnomonkey. Though hopefully he does by now because this thread is from 2011 ;)
smh...This is a 6 YEAR old tread with a server that uses Ultrawide SCSI Drivers. The server held a total of 6 drives. the max i think these guy went was to 73GB so he would only be building a second RAID of the same size.


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