Troubling fsck_hfs -Sd (block scan, debug) output. Help me understand. (PARTIALLY SOLVED)
I wanted to scan my backup drive for bad blocks, so followed a suggestion to do so with fsck_hfs.
I don't know what to make of the output of this:
18-03-04 MacBookPro% sudo fsck_hfs -Sdfy -c 16m /dev/rdisk5
journal_replay(/dev/disk5) returned 22
** /dev/rdisk5
Using cacheBlockSize=32K cacheTotalBlock=1024 cacheSize=32768K.
Scanning entire disk for bad blocks
Executing fsck_hfs (version hfs-366.70.3).
Block 2 is not an MDB or Volume Header
Block 7814037166 is not an MDB or Volume Header
volumeType is 0
0000:
0000 0000 0000 0000 0000 0000 0000 0000 |................|
. . .
01b0:
0000 0000 0000 0000 0000 0000 0000 00fe |................|
01c0:
ffff eefe ffff 0100 0000 d517 383a 0000 |............8...|
01d0:
0000 0000 0000 0000 0000 0000 0000 0000 |................|
. . .
01f0:
0000 0000 0000 0000 0000 0000 0000 55aa |..............U.|
unknown volume type
primary MDB is at block 0 0x00
alternate MDB is at block 0 0x00
primary VHB is at block 0 0x00
alternate VHB is at block 0 0x00
sector size = 512 0x200
VolumeObject flags = 0x01
total sectors for volume = 7814037168 0x1d1c0beb0
total sectors for embedded volume = 0 0x00
CheckForClean - unknown volume type
CheckHFS returned 6, fsmodified = 0
SORT OF SOLVED:
Looking again at the arguments I gave -
-Sdfy -c 16m
-d Display debugging information. This option may provide useful information when fsck_hfs cannot repair a damaged file system.
-S Cause fsck_hfs to scan the entire device looking for I/O errors. It will attempt to map the blocks with errors to names...
-y Always attempt to repair any damage that is found.
-f ... force fsck_hfs to check and repair ...
I am reminded that I included -d. (I entered the command a few days ago, and just saw the results.)
So I am probably looking at debug output that I can largely ignore since it ends in "fsmodified = 0" which suggests no bad blocks were found, and I pointed it at an entire drive (which isn't HFS+ by definition, rather than at an HFS+ partition on said drive).