Antony Mawer wrote:
Is it recommended/required to do something like:
dd if=/dev/zero of=/dev/ad0 bs=1m
before use to ensure the drive's sector remappings are all in place,
before then doing a newfs?
It seems logical to read the whole device first with "conv=noerror" to
be sure the drive has encountered and noted any correctable or
uncorrectable errors present.
Only then write the entire drive, allowing it to remap any noted bad
sectors. i.e.:
# dd if=/dev/ad0 of=/dev/null bs=64k conv=noerror
# dd if=/dev/zero of=/dev/ad0 bs=64k
The problem is that when dd hits the first bad sector, the whole 64k
block containing the sector will be skipped. There could be more bad
sectors there... or none... If you hit errors I would re-read the
affected area with "bs=512" to get down to sector granularity.
I seem to recall a utility posted to a freebsd mailing list some time
ago that worked like dd(1), but would "divide and conquer" a block that
returned with a read error. Intent being to get the job done fast with
large blocks but still copy every sector possible off a failing drive by
reducing to sector-sized blocks if necessary.... Unfortunately I can't
find it now.
Joe Koberg
joe at osoft dot us
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