topic MOUNT/VERIFY cmd in Operating System - OpenVMS

MOUNT/VERIFY cmd

simon_164 — Thu, 20 Jan 2005 11:26:28 GMT

Dear All, what does the MOUNT/VERIFY command do ?

Re: MOUNT/VERIFY cmd

Joseph Huber_1 — Thu, 20 Jan 2005 11:40:46 GMT

There is no such qualifier to MOUNT.
Eventually You mean
MOUNT /[NO]MOUNT_VERIFICATION
or
SET VOLUME/[NO]MOUNT_VERIFICATION

?
It sets "Mount verification" for the volume,
mainly checks for errors on the volume, then blocks I/O until it recovers (device state "mount verification"), and informs operators about it.
Without mount verification, failures are detected only when a process accesses the volume.

Re: MOUNT/VERIFY cmd

Uwe Zessin — Thu, 20 Jan 2005 13:18:37 GMT

That's not quite correct, I am afraid.

Mount verification is from the age when disk drives used removable media (I know that that you are familiar with this stuff, Joseph). You could remove a 'pack' and replace it with a different one. In such a situation, a mount verification occured, all I/O to the volume was stalled and you were asked to replace it with the original one.

Later on, the stall mechanism of the mount verification was used for other things, e.g. during volume shadowing membership changes.

I have not tried it on recent versions of OpenVMS, but on earlier ones there was no 'mount verification polling' (or whatever you like to call it). Especially in an OpenVMS cluster it was possible that MVs of a volume occured many hours later - just when the disk drive was accessed again.

MV is a good thing, because it allows the user to recover from an error[*] - without it, I beleive, the volume is invalidated immediately.

[*] I once had somebody come in to the computer room, turn around is body and hit the RUN button of an RM03 disk drive which happened to be the system disk of a VAXcluster member. Fortunately I was present, heard the beeps from the LA120 consoles and could correct the problem. Pheww...

Re: MOUNT/VERIFY cmd

Robert Brooks_1 — Thu, 20 Jan 2005 16:31:47 GMT

Please do not mount a volume /NOMOUNT_VERIFICATION! I'm not suggesting that you are planning on doing this, but the notion of mount verification is needed for multipath failover. In other words, if you mount a device with /NOMOUNT_VERIFICATION and you have
a failure of the current path, you will NOT
get a transparent failover to another working path.

An example of a device that is NOT subject to mount verification is a foreign-mounted disk.

--Rob (Multipath engineer)

Re: MOUNT/VERIFY cmd

John Gillings — Thu, 20 Jan 2005 16:32:42 GMT

Uwe is correct. Mount verification is an historic mechanism which has been "hijacked" for different uses, most notably in shadowing. In general accepting the MOUNT default is the correct thing to do.

>Fortunately I was present, heard the beeps from the LA120 consoles and could correct the problem

We had a very recent incident where we moved a system from one lab to another. Curiously it wouldn't reboot - the console defined system disk was not present. On investigation, we found that someone had physically removed the system disk ONE WEEK before the move. It was accidental - they'd counted from the wrong end of the drive shelf. Despite lack of system disk and page file(!) there had been no apparent problems - the system had performed all its normal functions, obviously everything necessary from the system disk had been cached, and there was sufficient physical memory that paging was not required.

I'm not entirely certain if this is an example of the incredible resiliance of OpenVMS or a serious missing feature (like an LA120 complaining that the system disk has gone). ;-)

Re: MOUNT/VERIFY cmd

simon_164 — Fri, 21 Jan 2005 01:54:20 GMT

Thank you all for the replies,
apparently guys it's an old command. I have searched it in the DCL language book, the management 1, management 2 and the performance books with no success.
Do you have any full description about it?

Re: MOUNT/VERIFY cmd

Joseph Huber_1 — Fri, 21 Jan 2005 02:54:49 GMT

Of course Yes, my short answer of just watching for "failure" doesn't explain everything.

But the question of a command "MOUNT/VERIFY":
I don't remember (back to VMS 4) a change in the qualifier name: I think it was always /MOUNT_VERIFICATION,
there was never a /VERIFY.

Re: MOUNT/VERIFY cmd

Wim Van den Wyngaert — Fri, 21 Jan 2005 03:39:16 GMT

If your disks are MSCP served, it also allows the network guys to reorganise/boot their stuff (with network outages) without VMS going down because of a missing system disk. And it allows you to reboot the server that is serving the disk.

Wim