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ZIP and 4GB limit?

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Frequent Advisor

ZIP and 4GB limit?

I'm using zip 2.32 on OpenVMS 8.3, I64. We're using BACKUP to create disk-to-disk backups of the filesystem, and the resulting .BCK files are between 4 and 28GB. We do backup this up to another location, but I'd like to compress and keep some of them locally for convenience.

zip seems to be limited to 4GB. Is there a compression utility for OpenVMS I64 that overcomes this limit?
Steven Schweda
Honored Contributor

Re: ZIP and 4GB limit?

If you're compressing BACKUP save sets (and
you don't mind resetting the save set file
sttributes after expansion), then you could
use gzip (compression generally better than
Zip) or bzip2 (compression generally better
than gzip):


Both should be large-file capable.

The not-yet-released Zip 3.0 and UnZip 6.0
will offer large-file support. Pre-release
("BETA") source kits should be available


If you have a C compiler, and you don't mind
an occasional spurious warning from UnZip
(Look for "76 bytes"), then Zip 3.0e and
UnZip 6.00c should do the job.

There's some hope of seeing anouther round
of public beta code (Zip 3.0f, UnZip 6.00d?)
fairly soon, and even of the real release
before we're all dead. That should offer a
cure for the spurious warning from UnZip, and
even optional bzip2 compression instead of
Zip's default "deflate" compression.
Steven Schweda
Honored Contributor

Re: ZIP and 4GB limit?

And, by the way, I believe that Zip 2.x and
UnZip 5.x generally get into trouble at 2GB,
not (even) 4GB. (In some very old VAX
environments, size_t was unsigned, but lately
it tends to be signed everywhere, hence 2GB.)
Honored Contributor

Re: ZIP and 4GB limit?

There's a gzip port around that avoids this limit; it's what was used by HP for packaging various DVDs. For just this reason. Look on the OpenVMS Freeware, or elsewhere.

The field test of zip (V3) and unzip (V6) is the only way to go with the Info-Zip tools. There have been comments around about the implementation of compression in BACKUP, too.

And as a side note, consider turning off XOR on your BACKUP, as that BACKUP mechanism can lower the efficiency of zip compression.