I'm going to get my new small business database server in a couple days. It comes with one hard drive, but I plan on setting it up initially with a 3 disk RAID 5 system. Unfortunately, the extra drives won't be in for a few days after I get the server.

I'm using a hardware RAID controller. I want to get a head start on configuration. How "smart" is RAID in this sense? If I install and configure the OS on the single drive and then add the other two drives later to have it rebuild my data across the 3 disks?

If this is possible, is there any special procedure I need to follow?

  • Note that Linux software RAID can grow a RAID-5. You really do need to be more specific as to what RAID controller you're using... :-) – Captain Segfault Aug 4 '09 at 21:36

It depends on your RAID controller, but most likely it won't support that. It would have to move all the data around to lay it out in a clean way.

You best bet is to either be patient and wait for the other drives, or buy a 4th drive and then you'll have a spare for later.

If you buy a 4th, then you'll install on the one you have now, and then migrate the install over to the RAID once the other drives come in, using something simple like dd. Then that initial disk will be your spare.

  • I've had experiences with RAID controllers that supported this kind of migration. Some of the MegaRAID controllers can do this. There are also some that advertise the capability but a program to actually do the migration. That said make sure that you have backed up any data that you can't recreate. Rik – Rik Schneider Aug 1 '09 at 2:47

I would suggest the simplest way would be to run on that single drive till the others arrive. Then take an image of your working drive, configure your RAID array and restore the image.

  • +1 I agree this is the best solution. If your looking for imaging software thats opensource (free) look at Ghost 4 Linux and Clonezilla. It will do most file systems i.e. NTFS, ext3... – Nick Kavadias Aug 1 '09 at 5:30

Dell PERCs (a rebrand of LSI really) can do this - you need to set the first drive up as raid0 with just one disk, and then use the controller software (OMSA for Dell), to reconfigure the array.

But remember - when you add drives, the array size will increase, while the windows partition size will not, so you will be able to create a second partition on the added space, or try to expand the existing partition using diskpart, and that is very dangerous.

  • You're quite right, expanding a partition with diskpart is dangerous. Luckily there are a plenty of safe alternatives, such as gparted, partitionmagic, ext2fs anywhere, etc. – John Gardeniers Aug 1 '09 at 10:09
  • 1
    John Gardeniers: In my experience, none of these solutions is 100% safe, and none should be used on a live production system, at least not if you have the possibility of arranging proper downtime for backup>reinstall>restore or to reimage – dyasny Aug 1 '09 at 14:47

I don't think a generic controller would be OK with this. I'm not even thinking that a fancy array controller would be OK with this either.

Now, that said, you could start your work and then ghost or backup the machine to something like an external drive. Then scrub the system down, rebuild on the array, and restore.

That said, make sure you install your RAID drivers before you ghost the image. Not sure how well this will work, my spidey senses are telling me there is a 50/50 shot you will forget some detail and not be able to boot off the ghost image. Backup might be better, but you'll have to build up a basic enough system to restore from the backup, so not sure how much time that will save either.


It really depends on the raid controller and other factors. There is no automatic yes / no

I have seen some raid that let you just hot add / remove / swap resources like there is no tomorrow and others that use a bit of the hard drive space for various things such as the raid controller's database.

So, it really depends on the manufacturer.

Also, by adding the other drives, you will be changing the logic / size of the drive, that "may" cause other problems later on.

Personally to make sure you get no headaches later on, use the first few days just to muck around and get used to your new cool system, and then set up a raid from scratch and reinstall the server from scratch later.

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