We recently had a hard drive in a RAID die on us. We ordered the exact same model from ebay. A maxtor 6L200M0 200 gig drive.
It seems to be ok, but our old drives, the ones still in the raid, are 203000 bytes or so and this new one is 200000 bytes or so. Big difference. The cyclinders, heads etc all have different numbers as well.
The UDMA mode on the new one is 6 while the old ones are 5.
Is there anything we can do about this? Obviously we're not able to rebuild the array because the new drive is slightly smaller than the rest.
WARNING! Before doing any of the stuff below, read ALL the instructions on your RAID system and its software utilities so you know exactly what it can do, where to find the menu choices, and how to do it properly. Getting lost and searching in the middle of a data migration is potentially disastrous!
What type of RAID? I expect it was NOT a RAID0, or you would not be talking about rebuilding - lose one disk in a RAID0 and you've lost everything and have to re-start from scratch!
If it was RAID1 (mirrored drives) I would expect you can make it work. However, the simple way may not work. The "simple way" is you install the new drive in the failed one's place and tell the RAID controller to do all the rebuilding work for you. If you were really lucky in this case, that system might figure out that there is a way to do it if it simply re-sizes the area of the older larger drive to match. But I'm guessing it will not, and throw you an error message instead.
So, maybe you can force it. First step, without the new drive installed, would be to tell the RAID software to break up the RAID0 array and return it to a plain single drive with all of the data on the one good drive you have. Then you reboot. Now you have no RAID1 array.
Next step I would do is to pretend you are replacing the old drive with the new one. Use the new drive's supplier's software utilities to clone the old drive to the new one. You may need to set a few parameters, but what you want is to have it set up the partition on the new one to be the full size of the drive, and make it a bootable drive. You do the cloning, shut down and disconnect the OLD drive, and connect the NEW drive to the port that the old drive used to use. Reboot and your system will find and use as its C: boot drive the new one. Everything should be running fine on a machine that only has one drive (the new one).
Now you re-install the old drive as a second unit. To be safe, maybe you should check and write down the exact Partition size of the new drive. Then go into Disk Manager in Windows and re-partition the OLD drive to exactly that size, and format it. Now you have two drives with identical sizes, with one of them empty. (You will also have a tiny bit of unallocated space on the old drive. Simply ignore that - pretend it does not exist.)
Reboot and go into the RAID setup utilities. Tell it to create a new RAID1 array using the existing first drive with all your data plus adding in the second empty drive (used to be the "old drive"). This process of using one disk with all your data and adding a second disk to make a RAID1 array is standard stuff for RAID installation. Hopefully when it finds that the second drive is exactly the same size as the existing one, it will comply with your orders. Shazamm! Well, I hope so!
Now, I presumed your problem was in a RAID1. Maybe it was RAID5 with multiple drives. In that case my procedure above is entirely wrong, and you should IGNORE IT! Then I'd go back to reading all the RAID system documentation to check for loopholes. You say it cannot rebuild the array because the replacement drive is slightly too small. Have you actually tried it and got an error message? If so, does the documentation suggest a work-around for this situation?
If not, I can suggest two paths. One is to go searching again for an identical replacement drive, this time knowing that you need a particular version of it, not just the same model number. The other is to do a process similar to what I outlined above. COMPLETELY back up all your data, OS, Registry - everything! - from the existing array to an image and verify that it is a complete good copy. Then DO IT AGAIN, including the verification, onto another device, portable HDD, or whatever. Now that you have two known-good copies of everything, it would be safe to re-partition every drive you have to the same size to match the new replacement, then create the new RAID5 array from them all and restore from the backup.