SC3 bit

Question

what SC3 bit and its importance with respect to mapping & masking

xe2sdc · Accepted Answer

Santhosh both SC3 and SPC2 have little if nothing to do with mapping and masking since they both are "FA flags" that you can enable (as you already know from Mike's posts) either in the binfile or via symmask commands. Both flags changes to some degree the way the FA port will behave while "talking" to your hosts. You can change this behaviour either for all the hosts connected to the processor (via binfile change) or only for some of the hosts (via symmask commands). Our Support Matrix clearly explain when to enable (or disable) SC3 or SPC2 since both those flags have -as almost everything- drawbacks.

When an host sends scsi commands (reads and writes) to the storage, it follows directions supplied by the T10 consortium. There are different documents that explain different aspects of the SCSI protocol. When working with disks one of the most important document is the one that explain the SBC (scsi block commands). Another very interesting document is the one that explain the SPC (scsi primary commands), a common set of commands that every SCSI target should implement. As with every protocol, there are different versions and usually recent versions offer everything that was already present in previous versions and add some new features.

Following SPC and SBC (and their different revisions) can be a challenging task for O.S. vendors .. Just like any other standard, SCSI offers a lot of different ways of implementing the protocol .. And each and every vendor have its own implementation. The Symm/DMX have to deal with all of them and have to be flexible.

SC3 a bright example of the flexibility of the DMX

The code itself will ALWAYS understand SCSI3 commands. But will USUALLY qualify itself as SCSI-2 compliant. Since sometimes the hosts can be "fooled" when the storage qualifies itself as SCSI-3 compliant, the code chooses to qualify itself as SCSI-2 compliant BY DEFAULT. That's the key ..

.. If you want (for a given host or set of hosts) you can ask the DMX to qualify itself as a SCSI-3 compliant target. That's why you have to enable SC3 only for selected and tested hosts and not for everyone. That's why you have to enable SC3 for AIX hosts or for SunCluster hosts

.. Since those hosts DO REQUIRE a SCSI-3 compliant target, the DMX will qualify -ONLY FOR THEM- as SCSI-3 compliant.

SPC-2 is almost the same .. the main difference is that SPC-2 will qualify the target as a SPC-2 compliant host while SC3 will qualify the target as a SBC-3 compliant target

.. the default is obviously a SPC (version 1) and SBC-2 compliant target

Is it clear ?? I think it's everything but clear .. But you asked .. and here we are

Message was edited by:
Stefano Del Corno

MikeMac1 · Answer

The SC3 bit is used to support SCSI-3. What type of host are you using? It's use is dependent on host type.

SKT2 · Answer

the host invloved is HP-UX 11.11 which is SCSI2 supported.. HP-UX 11.31 onwards suppor the SCSI3 protocol.. which also supports the more than 255 ext_bus instances..

so my server SPC (version 1) and SBC-2 are the right one..

xe2sdc · Answer

Santhosh don't use your own calculator to do the math ..

EMC supports only "allowed" configurations .. And they are clearly stated in our Support Matrix. Nowhere else. It's up to EMC to tell you how to configure our storage. Don't trust vendor's claims .. Look ONLY EMC SUPPORT MATRIX.

xe2sdc · Answer

Santhosh both SC3 and SPC2 have little if nothing to
do with mapping and masking since they both are "FA
flags" that you can enable (as you already know from
Mike's posts) either in the binfile or via symmask
commands. Both flags changes to some degree the way
the FA port will behave while "talking" to your
hosts.

Please note however that some FA Flags DO affect the way you map your devices. And HPUX with its VolumeSet Addressing (V-bit on the FA side) is a bright example. If you enable V bit on the port via a binfile change, you'll map devices supplying vbus,tgt,lun values. If yuo disable V bit via binfile, you'll map devices supplying only the "lun" value. Please note however that if you modify the v-bit via symcli commands (symmask) you still have to map the volumes according to the binfile configuration of the processor.

samaks · Answer

Hi,All about SCSI is very helpful, thanks.I am using AIX 5.3 hosts with DMX3. In the support matrix(E-Lab Navigator) Director Bit Information part, there were no SC3 flag to be set for our hosts when setting up the hosts. So I didnt set anything and it works fine. Is there anything wrong with that? Does it change according to the HBA model, server model or it only depends on it is AIX or not?And if I have to change the flag, does it have a disruptive effect like setting the SPC-2 flag?Regards.

RRR · Answer

I must admit I don't remember seeing any SC3 flag as well and we have quite a bunch of AIX's attached to our DMX3's.

BrianMarsh · Answer

I understand from various postings and the whitepaper "White Paper: Enabling SPC-2 Compliancy on EMC Symmetrix DMX Devices Connected to VMware VI3 Environments - Applied Technology" how enabling the SCSI-2 flag can be disruptive.

How about if the SPC-2 flag is set on the director and a running host needs the SC3 bit set (using symmask set hba_flags). Would this be disruptive in the same way or transparent ?

Our situation is a VMWare ESX 3.0 server currently connected to a Clariion that we are going to also connect to a DMX3 (5771.105+).

xe2sdc · Answer

Changing FA flags (via symmask set hba_flags) usually requires you to reboot your host. The real reason for the reboot is that from FA perspective you need the HBA to log out and log in again. However, from the host perspective, changing the "capabilities" of the storage may require some sort of rescan of the hardware. And usually such rescan takes place at boot time. Rebooting will meet both points of view .. the hba will log off and log on .. and the host will rescan the storage

This obviously apply to both SC3 and SPC2

Message was edited by:
Stefano Del Corno (Happy Easter!)

wishtobeMrEMC · Answer

Stefanofirst of all, many thanks for detailed explanation about SC3 bit .. As SC3 bit flag can be set either for specific hosts or all hosts by either symcli or in bin file, pls share us how it should be done for knowledge sake. I do understand that bin file config change should only be done by EMC experts thanks

xe2sdc · Answer

If you look at Brian's post, you'll see that he quoted a paper: "White Paper: Enabling SPC-2 Compliancy on EMC Symmetrix DMX Devices Connected to VMware VI3 Environments - Applied Technology".. You can read the paper and learn how to change SPC2 (or SC3 if you prefer) flag using either symmask (only for some hosts) or symconfigure (for all hosts).

Cheers ...

Symmetrix

SC3 bit

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