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Replacing RAID-5 disk drives without reinstalling OS.

Occasional Advisor

Replacing RAID-5 disk drives without reinstalling OS.

Hi everyone!

My server's specs.
HP Netserver LH3r
- MS Windows NT 4
- Installed Primary Cage
- RAID-5 with 5x9.1Gb HDDs
- 1 non-RAID HDD in slot number 6 of primary cage (standalone)

Now, the hard disk capacity is running low. We need to add on new hard disk drives to expand the overall disk space. Our main problem is we must not reinstall the OS, because this will result in the loss of customized software applications installed in the server. Reinstallation of these applications will overwrite the existing versions.

Is it possible to replace HDDs configured in RAID-5 without having to reinstall the OS? I was thinking about the possibilities of doing these:-

1. Remove drive no.1 from the RAID-5 config.

2. Physically remove it from the hot-swap cage.

3. Replace it with a new HDD (which is very much bigger in capacity, maybe 73GB).

4. Add the new drive to the existing RAID-5. Rebuild the RAID.

5. Repeat the same steps for drives 2 to 5 until all drives have been replaced.

Can these work? Will the overall capacity remain the same as before, or more?

Appreciate all the helps I can get.


Esteemed Contributor

Re: Replacing RAID-5 disk drives without reinstalling OS.

Although you can do what you describe, doing it may cause more problems that it solves. Let me explain.

Each drive in an array must be the same size. So, if you use a 36GB drive to replace a failed drive in an array of 18GB drives, then the extra 18GB capacity on that drive will not used by the array. So, replacing every drive in the array with a 36GB drive would result in n x 18GB of unused space on that array (where N = number of drives in array): your array would not be bigger.

If you went into the NOS: capacity would be unchanged because that unused drive space (N x 18GB) cannot be seen by the operating system until you make that space part of a hardware RAID.

But, you could go into NetRAID Assistant and use that free space to create a new RAID5 array.

After doing that, your operating system should see this additional space as an unformatted drive which you can then format and use to your heart's content. The capacity of this free space would be: n x 18-18GB (where you would subtract 18GB which is what this RAID5 array would use for parity) .

There is one serious problem with this. Since you are using the same set of 36GB drives for 2 RAID5 arrays, if you lose one drive, both arrays will go down, not just one. So, you have essentially doubled your chances for data catastrophe.

Is that clear? So, although you could do what you described, I don't think it is advisable.

What is your config? How many arrays do you have set up? Are your OS and data on separate RAID arrays? Or, if not, are they at least on separate partitions?

It might be better to use Ghost or some other imaging software to preserve your customized software:
1. Create a disk image of the OS partition (you can do a partition operation where it will just image the one partition instead of the whole logical drive).
2. TEST the image on a test system before blowing anything away. If you have another system that is identical, that would be ideal way to test it.
3. Then, back up data & TEST the backup to make sure it is good
4. once you are satisfied with your backups, then you could clear the array config, insert the new drive and use the image to put your NOS + customized software back on the server.

You might want to think about putting the OS on a different array from your data so it will be easier to expand data disk capacity in the future. A lot of people choose to install the NOS on a RAID1 mirror array of smaller drives (9GB or 18GB drives), then put their data on much larger drives in a RAID5 array (36GB or 73GB drives).

Now, I have never tried this, but there have been other people on this board who have successfully used Ghost to do this sort of thing. I think it's the only way you can save your customized software.

Anyone else have any thoughts on the matter?

Occasional Contributor

Re: Replacing RAID-5 disk drives without reinstalling OS.

This will not work. replacing the 18 GB drive with 73 GB drive will not make your raid any bigger.
The best bet is to use software like GHOST which will allow you to save the image of your raid and then restore it to large partition after you swap all the drives.
I think the other route is to use partition magic which will allow you to manipulate partitions but since I never used it I can't say for sure.

Andrew Bielecki