Replacing a Quorum Disk

[Volker Halle]

Jan,

to exit the IPC> interrupt, you need to enter (not C, which stands for: Cancel mount-verification)

The IPC (short for IPL C interrupt, where 0xC is IPL 12.) is described in the System Managers Manual Volume 1: Essentials

Chapter: Using Interrupt Priority Level C (IPC)

Volker.

[Eberhard Wacker]

Hi Volker,

I wouldn't had a doubt in such a configuration but many thanx for your poc. The reason I've asked is that I cannot test at the moment the whole scenario with the recreation of a virtual quorum disk. So I can only "believe" that the same will work.

One other point raised looking at your logfile: it can be handled in a smooth way only as long as mvtimeout has not been reached, right ?

Cheers,
Eberhard

[Eberhard Wacker]

Hi Wim,
what I miss is the possibility to use a quorum file on a HBVShadowed disk :-)
Cheers
Eberhard

[Uwe Zessin]

| >>> D SIRR C
|
| deposits hex C in the SIRR register, meaning set IPL 12

Hm, SIRR is the Software Interrupt Request Register - my understanding is that it requests an IPL 12 interrupt, but does not set the IPL to 12. Imagine what happens if the processor is currently running at a higher IPL - not a good idea!

Extra points if you know what fork processes are for ;-)

The next step would be:
>>> continue

| IPC> Q
|
| at IPC force Quorum recalculation
|
| IPC> C
|
| Continue normal operation.

Volker has already commented that "C" is used to cancel a mount verification.

| --- in a cluster, this HAS to be COMPLETED within RECNXINTERVAL

Right, and there must not be a bug in the VAX-8600 ;-)

| It has always been around, AFAIK, although
| the Vax syntax was slightly different.

>>> D/I 14 C

[Jan van den Ende]

Re Eberhard:


what I miss is the possibility to use a quorum file on a HBVShadowed disk :-)


Why is that not supported (and never will be !!):

Suppose a cluster with two equal halves (for ease of concept, take a two-site cluster, but the principle is general).

So, each halve has n votes, and there is a quorum vote. Expected_votes 2n + 1, quorum n + 1.

If the halves lose sight of each other, one halve has the qdsk, has quorum, and can continue; the other halve looses quorum.
The cluster integrity is guarded.
Now, suppose the qdsk is shadowed.
Again, the halves loose contact.
That could well mean that the shadow members loose contact.
Now EACH halve sees its member of the qdsk shadow set as THE qdsk.
Both halves maintain quorum, and within a few handfulls of IOs (say, miliseconds?) your data is seriously corrupted..
HPUX has a good descriptive name for that situation:
A "SPLIT BRAIN CLUSTER".
REALLY unwanted.
So: _NO_ shadowed quorum disk. Period.

hth

Proost.

Have one on me.

jpe

[Eberhard Wacker]

Re Jan:

sure, you're absolutely right, it will never be supported but nevertheless I would wish I COULD use a (one site located) shadowset as a quorum disk volume.

Also with the current (and long existing) VMS implementation I can set up the whole cluster in a non supported way so that cluster partitioning can occur (at least at boot time)!
So I still say: I would like to HAVE the possibility to use a shadowset as a quorum volume. If I set up the configuration in a way that can lead to trouble then this is my configuration failure in each case.

Cheers (and a proost)
Eberhard

[Eberhard Wacker]

Re Jan II:
- sysgen parameter quorum_disk remains as it is referring to a special disk
- this disk is a member of a shadowset
This would mean: no change to the current behaviour (but probably a lot of re-writing VMS code).
Simple(?) question: am I right or totally wrong ?
Proost
Eberhard

[Volker Halle]

re: last few

Setting SIRR to C requests an IPL 12. interrupt, which then will issue the IPC> prompt (running at IPL 12.)

Using the IPC mechanism in a SMP system, may lead to CPUSPINWAIT or CPUSANITY crashes, so AMDS is definitely the better choice ;-)

If the quorum disk has gone dead and MVTIMEOUT has expired, you can still DISMOUNT/ABORT it, IF no (other) open files are on that disk.

Shadowsets can split as well and if either side of the cluster then continues with it's local member ?! Just use a small quorum node, put it in a safe place and forget about it.

Volker.

[comarow]

Since you have availability manager, you do not need the IPC utility. Just reset quorum.


We have white papers on replacing a quroum disk. I'll email it to you.

[Ian Miller.]

Bob, if there is documentation on this then can it be on a public place (on itrc parhaps) and can you post a reply here with the link so people can find it in future.
Thanks,
Ian.