I see the following errors in dmesg:

wd0: (uncorrectable data error)
wd0a: error reading fsbn 2189695 of 2189664-2189695 (wd0 bn 2189695; cn
2172 tn 5 sn 4), retrying
wd0: (uncorrectable data error)
wd0a: error reading fsbn 2189695 of 2189664-2189695 (wd0 bn 2189695; cn
2172 tn 5 sn 4)wd0: (uncorrectable data error)

are they hardware or software error ?
that is, must I replace the hard-drive or should I only reformat the disk
and mkfs ?

is there any fsck-like command that would mark bad sectors so that there
are not used by the system (with or without reformatting) ?

TIA,
   Jo