[Info-vax] ZIP, UNZIP and BACKUP/COMPARE reporting %BACKUP-E-VERIFYERR

[Volker Halle]

I came across this problem, when testing a networker restore operation
on OpenVMS. How do they say: "don't test your backups, test your
restores" ;-)

If you create a simple sequential variable-length file, ZIP it and
UNZIP it, DIFFERENCES will be happy. But BACKUP/COMPARE will report
%BACKUP-E-VERIFYERR for the EOF block in those files.

A more detailled look (using DUMP) shows, that there is some data
after the EOF byte, which is not being preserved by ZIP/UNZIP (and
Networker for that matter), whereas an OpenVMS BACKUP (or an ABC/
Tivoli) backup/restore preserves this data.

One may argue, that 'well-behaved' applications should not store any
data AFTER the EOF byte, but this cannot be prevented. This 'feature'
will not be noticed until after you have to restore the file from some
backup tool, which does not preserve that information. But then it's
too late...

See below for a reproducer and some more details,

Volker.


AXPVMS $ cre test.dat
VMS
<ctrl-z>
AXPVMS $ zip test test.dat
  adding: TEST.DAT (stored 0%)
AXPVMS $ unzip test
Archive:  USERDISK1:[HALLE.TEST]TEST.ZIP;1
replace test.dat? [y]es, [n]o, [A]ll, [N]one, [r]ename: r
new name: test.dat_r
 extracting: USERDISK1:<HALLE.TEST>TEST.DAT_R;

AXPVMS $ diff test.dat test.dat_r
Number of difference sections found: 0
Number of difference records found: 0

DIFFERENCES /IGNORE=()/MERGED=1-
    USERDISK1:<HALLE.TEST>TEST.DAT;1-
    USERDISK1:<HALLE.TEST>TEST.DAT_R;1

AXPVMS $ back/compare test.dat test.dat_r
%BACKUP-E-VERIFYERR, verification error for block 1 of USERDISK1:
[HALLE.TEST]TEST.DAT_R;1

AXPVMS $ dump test.dat
...
Virtual block number 1 (00000001), 512 (0200) bytes

 00000000 00000000 FFFF0053 4D560003 ..VMS........... 000000
...
AXPVMS $ dump test.dat_r/head
...
        End of file block:                1
        End of file byte:                 4
...
Virtual block number 1 (00000001), 512 (0200) bytes

 00000000 00000000 00000000 0A534D56 VMS............. 000000

Note the 'FFFF' at byte 6 and 7 in the original file whereas those 2
btyes in the
unzipped file show '0000'

AXPVMS $ unzip
UnZip 5.51 of 22 May 2004, by Info-ZIP.  For more details see: unzip -
v.
AXPVMS $ zip
Copyright (C) 1990-1999 Info-ZIP
Type 'zip "-L"' for software license.
Zip 2.3 (November 29th 1999). Usage: zip=="$disk:[dir]zip.exe"