From: Lee Penn  <lee@dlpco.COM>
Subject: Re: Tape backup revisited/CTAR/Tape verify
Resent-From: mmdf@xenitec.on.ca
Submit-To: scogen@xenitec.on.ca
Organization: [resent by] The SCOGEN gateway and Propagation Society
Date: Thu, 23 Jul 1992 11:23:56 GMT
Precedence: bulk

>I see that  you are becoming fast friends with tar
>and tape backups.  In my experience with our clients
>at Lynk Systems, my previous employer, tape backups
>are always fine until you need them, and then the
>backup tape(s) with the oldest data, is, of course,
>the only one that gives a return error code of zero.

>Do you verify your backups after you do them ?
>We automate backups using cron, and then verify
>the backup afterwards.  It might take hours
>and hours, but whatgood is a back up if it is
>corrupted.

Ctar does the above automatically and leaves a selected user 
email regarding the results.  Your verify does not do a bit level 
compare to the actual files.  Therefore how do you know that the 
data is REALLY good?  Ctar DOES a bit level compare verify.

>I don't understand why you are raving about CTAR
>though.  I have no experience with it, but you
>said that it wouldn't proceed past a bad spot on
>the tape.  I don't want to rub it in, but you can
>use dd to go past a bad spot.  Don't try this
>though unless you have no other recourse.
>Also you must use the no-rewind tape device,
>and it must all be done from within the same shell.

No, dd would not go past the bad spot.  Do not know why, but I 
tried all the tricks you mention.  The tape would just spin 
backward and forward endlessly finally giving an error code.  
There was absolutely NO way I could force it bad the bad spot.
I did use /dev/nrct0!

>I think that  as long as tape backups depend on
>error correction schemes that use checksums, we
>will always have problems.  I am looking for a
>backup program that uses CRC.  Do you know of any ?

There may be some.  Ctar, by design supports the tar format and 
will process tar backups just fine.  This is a nice compatibility 
touch.  Frankly, I would like to see crc in the controller 
hardware.  OR... maybe even the driver for the tape.

>rjs@crs.cl.msu.edu
==============================================
Please read the following info from Tom Podnar @ Microlite
==============================================
COMMON RESPONSE BY UNIX GURU WHEN TOLD ABOUT CTAR:

>> But of course you can do the same thing if you back up with `cpio' and
>> create a boot and root system floppy using the SCO utility 
>> `mkdev fd'.  I had some intensive experience with this process when
>> I tried to install ODT 1.1 on a SCSI disk with more than one gigabyte.
>> There are no warnings, but when you try to write past one gigabyte you
>> wrap the disk producing results just like the Michelangelo virus!
>> There is a fix for this and I believe the problem is corrected in
>> ODT 2.0.
>> Paul Budnik

RESPONSE TO UNIX GURU IS:

Interesting. We get a response like yours just about every time we post
anything about our product.  We kind of place it in the same category of:

   My VI and nroff are so good, why would I ever consider bying a
   WordPerfect or a FrameMaker.
        or
   AWK can be used to make great spreadsheets.  Why buy Lotus 123?

I guess we'll never sell the UNIX gurus like you a copy of our product,
but then you aren't our target market, anyway.  We're after the people
who have to prepare for disasters and would have no earthly idea what
to do if they ever saw the prompt on an SCO emergency boot diskette.

I would leave you with the following thoughts about the differences between
our product and doing it ``the old fashioned way''.

A) Our product automatically backed up the system every night, performed
   a bit level verification, and mailed you the results of the operation.
   We even COMPRESSED the backup if we had to. So you are now POSITIVE
   that the backup you performed is really there.  Do you trust your
   cpio backup implicitly?

B) When you made your SCO disks, what happened when your /dev/ directory
   was hopelessly too large to fit on one filesystem diskette (Oh, you
   say you made it THIS TIME?)

C) What!, you say that DKINIT isn't on the floppy, or doesn't work at all
   since you are running 3.2v4.0? What will you do now?

D) Now what did your drive parameter, fdisk, and divvy partitions look like?
   And where WERE those filesystems mounted?
   Bet you wish you had our CT-BOOT Hard Disk Status Report to refer to.

E) Now is your divvy syntax divvy -b 1 -c 1 -p 0, or was that
   divvy -b 45 -c 45 -p 3 -m, or was it just divvy /dev/dsk/6s0?
   These systems with multiple hard drives are sure a lot harder to
   rebuild when you have to know the EXACT syntax for each command.
   CT-BOOT, of course, knows the answers and makes them push button
   simple.

F) OK, your root filesystem is corrupt and that's all you want to restore.
   How do you tell cpio to automatically exclude any files that were on
   other mounted filesystems.  CT-BOOT can do this, and will automatically
   exclude any directories that were network mounted at the time you did
   the backup.

Well, you get the point. THESE are the kinds of things that make CTAR and
CT-BOOT a special combination. Nothing available combines all the things
we do into such a sensible, user friendly product.  In closing I am
placing a copy of the CT-BOOT Hard Disk Status Report at the bottom of this
file.

===============================================================================
  Microlite Corporation                        CT-BOOT HARD DISK STATUS REPORT
  ____________________________________________________________________________

  REPORT FOR :  SCO UNIX Release 3.2v2.0                              Page:  1
                System Name: mlite   Serial: sco001304
  REPORT DATE:  Mon Jun 29 16:12:14 EDT 1992

  DEVICE NAME:  /dev/rhd00  (Primary Hard Drive - Type = SCSI)


    STORAGE CAPACITY

      Megabytes(MB):   632  Kilobytes(KB):    647168  Bytes:    662700032


    PHYSICAL LAYOUT [ /bin/dparam /dev/rhd00 ]

      Cylinders   :    632       Heads            :     64
      Write Reduce:      0       Write Precomp    :      0
      Ecc         :      0       Control          :      0
      Landing Zone:      0       Sectors Per Track:     32


    PARTITION LAYOUT  (1 Track = 16KB) [ /etc/fdisk -f /dev/rhd00 ]

      ----- Partition ------    Track    Track    Track
      Num     Type    Status    Start      End     Size
      ___  _______  ________  _______  _______  _______

        1  UNIX     Active        640    40383    39744
        4  DOS      Inactive        1      639      639


    FILE SYSTEM LAYOUT  (1 Block = 1KB) [ /etc/divvy -b 1 -c 1 ]

      Name          Type          #  First Block   Last Block  |         Size
      ____________  ____________  _  ___________  ___________  |  ___________
                                                               |
      Sdisk0        AFS           0        32768       225268  |       192501
      swap          NON FS        1            0        32767  |        32768
      u             AFS           2       225269       634868  |       409600
                    NOT USED      3            -            -  |            -
                    NOT USED      4            -            -  |            -
                    NOT USED      5            -            -  |            -
      recover       NON FS        6       634869       634878  |           10
      hd0a          WHOLE DISK    7            0       635903  |       635904

    Warning: Sdisk0, root are names for same partition


    MOUNTED FILESYSTEMS

      Mount Directory             Filesystem                  Size (KB)
      ________________________    ________________________    _________

      /                           /dev/root                      192501
      /u                          /dev/u                         409600
=================================================================================
================================================================================
Lee Penn,  DLP Technologies, Inc.                     Voice: 513 232-7791
SCO Advanced Product Center                           FAX: (513) 232-7801
7444 Jager Ct.
Cincinnati, OH  45230-4344                           email: lee@dlpco.COM

Newsgroups: biz.sco.general