e2fsck discrepancies

[Roland Bock <rbock eudoxos de>]

Hi,

yesterday I ran e2fsck -n on a mounted file system and got:

/dev/sdb1 contains a file system with errors, check forced.

According to Ted, the lines that followed were not to be trusted due to 
the fact that the file system was mounted. But this error statement 
suggests to run a check with the fs unmounted.

Today, we scheduled a downtime and ran the check. It came of completely 
clean:
~: e2fsck -fy /dev/sdb1

e2fsck 1.40.8 (13-Mar-2008)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdb1: 32028520/536870912 files (0.5% non-contiguous), 
802465197/2147460933 blocks


Does this mean that read-only checks are generally not trustworthy, even 
the statement that the filesystem has errors? Or something like

Read-only reports clean: fine
Read-only reports error: not necessarily really an error


Thanks and regards,

Roland