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I'm running a SBS 2003 server which uses Microsofts software RAID, mirroring mode. A few days ago, one of the disks started to show problems, and a new one was aquired. However, I can't get it to replace the old one (The disks are same make and size).

(Note: I'm running a swedish version, so any names might be off, I'm transguesslating here...) In the disk manager, when right-clicking the running disk (Disk 2), "Add mirror" is greyed out. The new disk (Disk 1) is initialized, and converted to dynamic, but has no volume on it. The old disk now has a single, standard (simple?) volume on it, after breaking the old mirroring.

Why can't I add a mirror?

EDIT: Seems same make and size does not correspond to same physical size. The old disk is all of 1 MB larger than the new one. I can see the same thing on another mirrored disk, one of them is 1 MB smaller than the other. Could this be related to which disk was the original "master" of the mirroring? In both cases the higher numbered disk seems to be larger.

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up vote 0 down vote accepted

If the new disk is even slightly smaller than the new one, you will not be able to create the mirror, which looks like what is happening here. If you mirror the smaller disk onto the larger, then all will be fine, however what you are trying to do here is mirror the larger disk on to the smaller, which will not work.

Your only option looks to be to get another disk that is the same size (or better bigger).

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Getting a 2 TB disk instead of a 1 TB one because of this seems silly. Seems to be simpler to just copy the "larger" disk to the smaller one and then do the mirroring in that direction? – carlpett Feb 15 '11 at 12:04
@carlpett If that's what you want to do then go for it. I suggest getting a bigger disk because disks are cheap (ish) and it is a case of plugin and go. My time is worth more than a disk with some wasted space. – Sam Feb 15 '11 at 12:17

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