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DISKSCAN.DOC
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1991-04-30
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DISKSCAN Charles Petzold
Purpose: Locates and identifies disk errors on hard and floppy disks, Bernoulli
Boxes or other similar storage devices.
Format: DISKSCAN [d:]
Remarks: The DOS "Abort, Retry, Ignore?" and the CHKDSK "x lost clusters found"
messages tend to appear after it is too late to save possibly
valuable data. Regular use of DISKSCAN will show when a hard disk is
beginning to go bad--for example, when a specific sector or two in an
as-yet unallocated cluster has become unusable since the disk was
formatted. (DOS marks and does not use bad clusters it finds while
formatting. DISKSCAN reports these "Flagged as bad.")
DISKSCAN error messages include:
CRC Error: Data checksum as recalculated during read does not agree
with checksum stored on disk when written.
Sector Not Found: Sector boundary created during formatting is no
longer readable.
File Alloc. Table and Can't Read FAT: Very serious error: Back up
what you can with COPY and reformat disk before trying to put
files back on it.
Boot Sector: If this sector of a hard disk goes bad, put a DOS disk
in drive A: and issue SYS C: command. Then COPY COMMAND.COM C:.
This will put a fresh copy of the system files on drive C:. If
this does not work, boot up again from the external DOS floppy
disk, back up all hard disk files, and reformat the hard disk.
Root Directory: Errors here could keep you from later being able to
load a file or save updates to it. CHKDSK will probably indicate
unallocated cluster chains or cross-linked files, and you may
have to use CHKDSK/F to save what you can.
Unallocated: As yet, not serious, as the bad sector is not being
used. When it is, though, and you try to save a file with this
sector, you'll get an "Abort, Retry, Ignore" message. Select
"Ignore" to save what you can, then REName the file and save
again under the new name. Use RECOVER filename with the original
file; this will cause DOS to flag its cluster(s) as bad.
(DISKSCAN does not enter the bad cluster numbers in the File
Allocation Table; FORMAT and RECOVER do.) Then delete the
original (RECOVERed) filename and check the second version you
saved (under the new name) to see how much (if any) of it is
usable.
Used by file: While DISKSCAN reports the bad sector number, it does
not do a cross- check to see which of your files is using that
sector. You may be able to identify this by issuing the command
SWEEP COPY *.* NUL
When COPY encounters the file with the bad sector it will report
"Abort, Retry, Ignore." Note the bad file and press "I" to
continue.
Read Fault and General Failure: The sectors so designated are bad,
but the errors reported don't fall into any of the above
categories.