Question on VCM Device.

Question

Hi,

I have read on the forum, but am still a little confused if its ok if the VCM Device is not mapped with all the FAs.

Went through emc204637 and found the following paragraph:

if the VCM gatekeeper is assigned to multiple fibre or iSCSI paths, you are therefore potentially sharing a write enabled volume between different hosts and different host types. This has caused data corruption and crashed hosts. (The impact depends on the host data/host label written to the VCMDB volume and the different host types involved.) If the VCM gatekeeper is assigned to multiple host paths, one avoidance is to manually set the assigned VCM gatekeeper volume write disabled on the fibre or iSCSI paths via Solutions Enabler commands* or via EMC Inlines commands. This avoidance does NOT affect device masking operations. However, this is not a permanent fix, as the volume may become write enabled on these paths again. Therefore, the Best Practice recommendation is never sharing the VCM or ACLX gatekeeper between multiple hosts and assigning only the VCM or ACLX gatekeeper volume to the Administration Host.

Does this mean that I should not mask the VCM with more than one Hosts [SAN Mgmt Hosts I guess] or more than on FA ? The term "path" is causing the confusion. The paragraph after that sound like its talking about hosts, but just wanted to be sure.

Also, if the VCM device is not mapped with all the FAs, and the only FA its mapped with goes down, what happens to the symmaskdb updates ?

The Primus also states that for DMX-3 and 5771 onwards it doesnt matter if the VCM is mapped to all the FAs or not, but what about say DMX1/2000 with 5671 ?

In the output below.

symcfg -sid 1234 -dir 4C -p 1 -v list |findstr "(SPC2) (SC3) (OS2007) (C) VCM"

Device Masking (VCM) Config State : Enabled

VCMdb Access Restricted State : Disabled

Common_Serial_Number(C) : Enabled

SCSI_3(SC3) : Disabled

SPC2_Protocol_Version(SPC2) : Disabled

SCSI_Support1(OS2007) : Disabled

VCM_State(VCM) : Enabled

Does the second highlighted line is something I should worry about ? Does VCMdb Access Restricted State : Disabled indicate that VCM is not enabled in some way ?

Sorry for the barrage of questions, but would be thankful if someone could help.

mamer1 · Answer

I've looked at our settings (we have DMX3s and DMX4s).

Device Masking (VCM) Config State : Enabled

VCMdb Access Restricted State : N/A

In other Questions for the DMX3 and 4s;

A VCM device can be mapped and masked to multiple FA's and Hosts. Note that the number of masked hosts should be minimal due to performance issues. We often map and mask at least 2 VCM devices to a host if neccessary. If no VCM device are specified, communication with the symmetrix will go through the current mapped and masked devices that are in use by the host. Someone correct me if i'm wrong.

As for DMX1s? I don't know how it's done there. Best you start a live chat on powerlink for the fastest answer.

dynamox · Answer

VCM and ACLX devices do not need to be masked, if a host is zoned to an FA that has VCM/ACLX device mapped to it, it will show up on the host automatically. On my DMX3 i unmapped VCM from all FAs except the ones that are used by my management hosts. Systems that do not see VCM device can not do any masking but they can still issue symcli commands using gatekeepers. For example i have a couple of Oracle boxes where they run nightly clones, i presented a couple of gatekeepers (3 cylinder device) and they do their thing.

take a look at this solution emc104861, it should answer your question about VCMdb restricted option.

dynamox · Answer

i think you are confusing VCM with gatekeepers

hpemc · Answer

Hi, Thanks for the explanation on this. I will go through the Primus article and let you know if I have any more doubts.

Symmetrix

Question on VCM Device.

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