[blue68f100]

10006 should be the first drive (ide 0) in the set with a SN 0x488A6DB662F7316C

Looking at the drive info, Drive 3 is already a 80 gig.

Idealy the drive should be the same mfg and model of the one be replaced. Capacity should be within 2-3 % of the original one.

Backup you data ALWAYS A GOOD IDEA.

Software raids are suppose to adjust to the smallest drive. But with this being the boot drive....... Only it knows.

Once the drives fails, you will not be able to access the data, till it has been replaced and rebuilt.

Plan :
Backup Data
powerdown
replace drive 1 (ide 0)
powerup
Snap will format and add OS files
Make drive a HOT Spare.
Should see it and start the rebuild.
It is a good idea to restrict access during the rebuild process, but not mandantory, will be extremely slow.

If you want to up the capacity all data will be lost. You can not up the capacity with our re-formating. Install 4 new 120, allow it to do its thing then. Then transfer data back.