[Info-vax] analyze/disk errors

[tadamsmar]

On Thursday, December 5, 2013 1:45:58 PM UTC-5, hb wrote:
> On 12/05/2013 05:16 PM, tadamsmar wrote:
> 
> > ANAL/DISK gave me a this warning ANALDISK-W-MAPAREA on BADBLK.SYS and some other files.
> 
> 
> 
> I don't know what analyze/disk is checking and what makes it issue such
> 
> a "warning". If the map area is invalid or even corrupted as
> 
> help/message states, then you usually can not get away with copying the
> 
> file contents: the map area describes the disk blocks containing the
> 
> file data. Ask your friend backup to restore the "some other files".
> 
> 
> 
> > ... So I tried to do copy it.  Copying worked on the other files, but I got an error when I tried to copy BADBLK.SYS....
> 
> 
> 
> Besides any map area problem, that's expected or the "nature" of
> 
> BADBLK.SYS: it contains/maps all the disk blocks which are not
> 
> guaranteed to be read. Mapping is done on the disk cluster base, so
> 
> there may be some good and some bad blocks. As far as I know, todays
> 
> disks do bad block replacement so, as long as that works, there should
> 
> not be real bad disk blocks in that file. But BADBLK.SYS may contain
> 
> "the end" of the disk. Consider a disk with 1000 blocks and a cluster
> 
> size of 3. Then BADBLK.SYS contains/maps one cluster, that is three disk
> 
> blocks starting at logical block number (zero based) 999. That's all
> 
> normal (no ANALDISK-W-MAPAREA) and expected as well as an error when
> 
> trying to copy such a BADBLK.SYS.
> 
> 
> 
> > So I made an image backup and restored the image from that backup and that cleared up the warning on BADBLK.SYS.
> 
> 
> 
> Because an image backup only contains the file header of the BADBLK.SYS
> 
> and a new BADBLK.SYS is created by backup when it restores the image
> 
> backup and implicitly initializes the disk (or by an explicit init
> 
> command if the restore is done with the /noinitialize).
> 
> 
> 
> And now, for fun, try to copy BADBLK.SYS to NLA0:. Any error?
There the HELP/MESSAGE on the MAPAREA error:


 MAPAREA,  file ('file-id') 'file-name' invalid map area

  Facility:     ANALDISK, Analyze/Disk_Structure Utility

  Explanation:  The specified file has a corrupted map area.

  User Action:  The damage can probably be repaired by copying the file to
                a new version and deleting the original version. It might be
                necessary to reconstruct the file from backup media.

I just followed the instructions.

A number of you seem to think that the VMS documentation is full of bull.