Daniel Quinlan wrote:

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You can get back your 4GB spare, since you only need one spare. The spare only has to be the same size of the largest data disk in the system. If you have a 9GB spare and a 4GB disk fails, you end up adding 5 GB to the filesystem when the spare replaces the failed disk.

kls@netapp.com (Karl Swartz) writes:

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No, you end up putting 4GB on a 9GB drive and getting no more space in the file system than you had before. (If there are multiple spares in the system, the smallest one which is large enough to replace the failed drive will be used.)

That's a shame.

Is this information documented somewhere?

Yes, exactly where you'd expect, in the System Administrator's Guide's chapter on Managing Disks, under the section Using Disks of Various Sizes. It says:

When Replacing a Failed Disk

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If the new disk is larger than the old disk, however, the system can only use the same amount of space that was available on the old disk. For example, if you replace a 1-GB disk with a 2-GB disk, the extra 1 GB on the new disk will not be available to the file system. Therefore, it is most cost-effective to replace a disk with one of the same size.

This is on page 5-9 of the Release 3.1 SAG, one paragraph up from the bottom of the page. In the 4.0 version of the SAG, it's on page 9-9, same position.

The next page explains the "best fit" rule for selecting amongst hot spares of different sizes.

-- Karl