Was /CRC always in OpenVMS BACKUP command?

[Uwe Zessin]

> I can personally testify that I have seen /CRC recover a saveset in real situations,

Not possible. The CRC is stored in a longword in BACKUP's meta data. Redundancy group will provide the necessary 'overhead' to enable recovery.

Again, /CRC is usefull as an end-to-end check, because it covers the whole data path. Hey, I have even seen BACKUP creating corrupted save sets when the destination was on a remote DECnet node.

[Cass Witkowski]

I was orginally asking of the /CRC qualifier was always in the BACKUP command. I was hoping that some one had access to old documentation or remembered this fact.

I'm also curious what error message you receive when BACKUP detects an error when checking it's CRC error versus when the tape drive finds a parity error. Is there a different message?

As someone stated earlier the /CRC only detect erros it won't correct them.


Using DLT and newer tape drives has anyone experienced where the BACKUP CRC actually detected an error but the hardware did not?

Cass

[Uwe Zessin · Accepted solution]

HDRCRC, software header CRC error

Facility: BACKUP, Backup Utility

Explanation: An incorrect value occurred in the header CRC field

[Robert Gezelter]

Uwe,

Concur. The correction is done using the Redundancy Groups. One of the ways in which an error is detected is throught the CRC (my phrasing may not have been clear).

- Bob Gezelter, http://www.rlgsc.com

[Sheldon Smith]

I *do* remember.

The /CRC qualifier has always been there. We were excited when Backup finally came out. And, "Oh my god, look at these cool options!"
As mentioned earlier, the VAX had a CRC hardware instruction. And the developers were quite proud of that instruction! :)

[Uwe Zessin]

I was excited, too ;-)

After the upgrade to VAX/VMS V3.0 on the night from friday to saturday, I stumbled over a bug in the tape ACP. A simple
$ initialize MTA0: label
$ mount MTA0: label
$ copy file.1 MTA0:file.1

resulted in a fatal bugcheck :-(
On monday, our system manager (I worked on PCB designs back then) told me about BACKUP, so we regained the ability to transfer files between systems.

[Robert_Boyd]

I don't recall BACKUP being available on V3.0 -- unless I actually started with V2.x systems. I first managed a VAX 11/780 in 1981 and it was running the latest available. I remember in the early days I was still having to use the RSX compatibility mode disk backup utility before BACKUP came out. It was fairly soon after that when BACKUP came out ... much to my relief.

Robert

[Cass Witkowski]

Ok I got the first two questions answered as to when /CRC appear in the BACKUP command and what is the error message generated when the CRC does detect an error.

My thanks to all who responded.

Now has anyone ever received this error using DLT, SDLT, or ULTRIUM tape drives?

Cass

[Jan van den Ende]

Re: Robert,

That would pretty much pinpoint the timing:

I started at V3.2 in 1982 and it DEFINITELY was there then!

Proost.

Have one on me.

jpe

[Galen Tackett]

Though I don't have my VAX Architecture Reference Manual [Sites, 1998; chapter 4] handy as an authoritative source, I'm quite confident that the CRC instruction belonged to one of the architecture subsets omitted from the early MicroVAX systems least the MicroVAX I and II.

Just out of curiosity, does anybody know if any of the MicroVAX/VAXstation family ever did implement any of the subsets that weren't present in the early members of the family?