Bad magic number error indicates the system is mostly likely having trouble accessing VTOC (Volumne Table of Contents) This just indicates that the partition is in a strange state.
What to do when you saw bad magic number errors in Solaris? If you know the alternate superblocks, then you can fsck the partition. If you don’t know the alternate superblocks and created the partition using newfs command, then you can use the “-N” option to print out the superblocks without actually recreate the file system. For example:
newfs -N /dev/rdsk/c0t0d0s0
“format” tool might be able to correctly label the disk with valid VTOC. Relabel your disks essentially repartition the disks and existing data will be lost. A recommended approach is to run analyze feature in format utility. Analyze will try to verify or repair a bad sector on a disk. Please note that bad magic number errors doesn’t always translate to bad sectors. The physical disk might be working perfectly without errors.