VCM disk showing up on SAN attached host

When you need to connect a brand new host to the storage, you need at first to create the zones on the switches. But how can you know if the zones are working if you didn't yet mask volumes to the host ?? That's why the VCM exists
The VCM is a very special volume that is always available even if no explicit masking exists. It's enough to map the volume with the VCM flag and all the hosts zoned to the FAs will see this very special volume.

In good old DMX (DMX1 and DMX2) the VCM is still a volume (24, 48 or 96 cyls big) whith another very important role: it contains the symmask database itself .. Since it contains such an important database, it's kept Write Disabled just to be sure that nobody will tamper it.

In new DMX (DMX3 and DMX4) the database is in another area (SFS - Symmetrix File System) of the storage and you don't really need a volume where to put the database. But you still need a volume always visible. So the flag VCM still exists and is usually assigned to a GateKeeper that's mapped to all the ports of the DMX.

Just to return in topic .. It's normal to see the VCM device even if no masking exists. Solution Enabler is our software that allows you to manipulate VCM and masking .. But you don't need S.E. to "see" the VCM .. From your message I can tell you that you have a DMX1 or DMX2 (models ranges from 800 to 3000) since the VCM is still WD (while with newer boxes it's RW enabled since it's a GK). Now you know why it's WD

Cheers !!

Thanks. Stefano. so you seem to suggest VCM disk WOULD and SHOULD to be seen by every hosts that SAN attached and zones into the Symmetrx DMX?

what is confusing is at least in our enviroment that contains DMX1000( Mcode=5670) and DMX3000(Mcode=5671) , some hosts see the VCM disk,
some host don't. ( as checked via format ). any suggestions about why? would this maybe depending on solaris versions and/or HBA drivers ?

adding to the confusion is when the host does see the VCM disk, user or SA's will try to use this disk when they shouldn't.

Thanks for clarifying for me.
JasonJ

JasonJ .. when you zone your host, the VCM is the only volume you will see. And when you see the VCM you can say "OK the zoning is good, we can go on and mask some useful devices". Think to the VCM just like the way to verify that the zoning is good. It's also true that each and every FA needs the VCM to lookup the database, but however each and every host will see the VCM just as a proof that the zoning is good.

Message was edited by:
Stefano Del Corno

on VCM Ddisk ... "Since it contains such an important database, it's kept Write Disabled just to be sure that nobody will tamper it."

to clarify on the "Write Disabled" flag: does it means:
Write disabled for host, but still RW for DMX and FA directors?

Thanks.

Try to run "symdev show" against your vcmdb .. Usually a device is write disabled only on the frontend .... However don't pay too much attention to the status (write disable) of the vcmdb .. put more attention to its role and take great care not to mess with it via symmask commands

Can anyone tell me how to delete the VCM entry from the host.?

We have a AIX 5.3 OS and we decommisoned DMX luns from this server.Even I removed the zoning.

The User DOESNT WANT TO SEE the VCM 0000 lun when he runs the inq command.

Can you tell me how to disappear this lun ?

Since your host is a betrayer, it's a good idea to unplug all the fibres



If you really can see the VCM from our DMX, that means you still have at least a zone that goes from one of your HBA to an FA .. that's it.

The Host still have Zones but not zoned to DMX but ti HDS !

Do u want me to remove the fibre cables ! lol ..
What might be wrong here ?

If you removed the zones the host simply shouldn't see ANY device from the DMX

The VCM itself can not be hidden since you can't either "grant" or remove grant to an host. The VCM can be seen as long as the zoning is right. If you still can see the VCM (and you can show with the good old "dd" command its content) it's likely that the host still have zones

Trust me !!! THe host is not connected to DMX !!!

Anyways,I have asked the user to ignore this disk

Trust me .. if the host can REALLY see the VCM, you still have something in between that allows the host to see the VCM

Did you reboot the host after removing the zones going to the DMX ??

Usually switches do implement the so called "soft zoning" .. Google a little to find better details, however to keep things short, it's a zoning implemented in the Name Service that the switches do always offer. You simply define a list of wwns that can talk one to each other (a zone). When the HBA logs into the fabric, it will ask the Name Service "Who can I talk to, today?" And the NS will answer supplying the list you configured. But if you later change the zoning (in the NS) and the host doesn't ask again "Who can I talk to?" nothing will stop it from sending frames to previously allowed destinations.

Since you are absolutly sure that there is no active zone going from your host to the DMX and you are also absolutly sure that you can still see the VCM, the only idea that comes to my mind is that you are using the so called "soft zoning" (that's the default on almost every switch) and your host didn't log out and in again on the fabric.

If possible, try to reboot the host .. and hope it does work

Yes we always soft zone .

And hey I asked this query after rebooting the host !

If you still have Solution Enabler on the host, please run the following commands and show the output .. You wake up my curiosity !!

1) syminq | grep -i emc
2) symmask list hba
3) sympd list

ThX