At 12:59 PM 98/09/26 -0400, Bill Lancaster wrote:
...snip
>As does De-Frag/X from Lund.  However, it has alway been my contention that
>putting your data into the hands of a third-party vendor without having
>some protection mechanism is unwise.  (By way of example, regardless of the
>fact the I *implictly* trust Alfredo Rego and the gang at Adager, I'm sure
>I have backups before I do significant Adager functions.) This is why I
>will continue to recommend that no matter what disk maintenance product you
>use (De-Frag/X, DSM, or VOLUTIL), you should periodically run FSCHECK to
>verify the current status of your file system.  The CA ALL command within
>the program will do the trick.  I've had to say this probably a million
>times (so far) but using FSCHECK before and after using a disk maintenance
>product will pinpoint for you (and HP) what exactly caused any particular
>problem, should a problem arise.  For example, it is possible for extents
>to be cross-linked.  That is, an extent could inadvertantly have a forward
>or backward pointer (either to free space or to another file's extent) that
>doesn't belong to the file in question.  (This is a pretty rare problem but
>it *has* happened; enough so that precautions should be taken).  When a
>file is cross-linked it can ruin your whole day.  FSCHECK (and De-Frag/X)
>can detect this problem.  It would be wise at this point to have the
>Response Center assist you in fixing this kind of problem.
>
>My last point goes hand-in-hand with the FSCHECK issue.  That is, backups.
>I will also continue to recommend backups before running disk maintenance
>products in "update" mode.  This isn't because of and concerns about
>particular products but rather I believe it to be good operational
>procedure.

Very good points, as usual, made by Bill - particularly those about
involving the response center involvement and backups.

With respect to FSCHECK, one should take extreme caution when going there -
and thus the RC and backup advice.

In particular, there is a very insidious bug in FSCHECK's CD command (which
is indirectly invoked with the CA or CHECKALL command) which can result in
the loss of at least an entire group of files.

This bug has been fixed in 5.5 - but it's effects may still affect all
systems regardless of current MPE/iX level.

Essentially, to avoid any dire consequences associated with this bug,
instead of utilizing the CA command, use the following commands:

CD ;IGNORE (the IGNORE option is crutial here)

If no directory error follows, you may procede with the other commands that
comprise the CA set, namely CL and CE - or simply issue the CA command.

Otherwise, no not proceed. Or, if you must, ensure you have a good backup
and be prepared to restore some or many files.


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Gilles Schipper
GSA Inc.
HP3000 & HP9000 System Administration Specialists
300 John Street, Box 87651   Thornhill, ON Canada L3T 7R4
Voice: 905.889.3000     Fax: 905.889.3001
Internet:  [log in to unmask]
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