|I am confused. Your first post mentions "the the mirror seems corrupt". That would indicate RAID 1 mirroring. |
So your concern is the storage size and discrepancies when running chkdsk?
Are you running chkdsk without any switches ? Look at the link below.
One other thing, the 40GB is also a rounded off figure. Depending on the geometry of the drive it is probably more.
Is your disk formatted using NTFS or FAT32?
If using FAT32 and you write a file larger than 4GB you can generate a CRC error.
I suggest you run chkdsk with the appropriate switch/s to correct the discrepancy.