McNally
2 Bronze

When/Where to use SCSI-3 Flag

I'm looking for some advice from the forum on when and where to use the SCSI-3 Flag.  I'm implementing a few VMax arrays and EMC has the SCSI-3 flag enabled on all my FAs.  My understanding is that it doesn't hurt the host if the flag is enabled on the FA port, so as a best practice why not enable it for hosts that require it.  It's a better use to use the port override command to set SCSI-3 to disabled for hosts that have issues with the flag being enabled.

Thoughts?

When I'm creating LUNs, I also notice there is a box in the SMC to enable SCSI-3, so my question is: Do we have to enable SCSI-3 on both the port and the LUN, or is this just another level of granularity for enabling SCSI-3.

My standard environments are SUN, VMWare, Windows, AIX, and various Linux flavors.  Oracle is common as well as various clustering techniques.

Finally, what are the most common use cases people have seen for the SCSI-3 being required.

Thanks for your input.

6 Replies
sauravrohilla
4 Tellurium

Re: When/Where to use SCSI-3 Flag

Use of SCSI-3 Flags is totally dependent on the customers based on their requirements. I have seen so many customers have this bit disabled (or not enabled) on the FA and enable on individual initiators that requires it. So you need to find out how you are going to segregate your hosts? I think there are few hosts which might not like it (I cant tell that for sure) but its a requirement for Windows hosts. So its good if we enable it for the host (on the initiator level rather than on FA ports) but again that depends. If you want to segregate all Windows hosts on a seperate FA ports and Unix on a Seperate port. It all depends on how you want to proceed.

Also, SCSI-3 bit on the FA port and PER bit (SCSI reservation) on the LUN are two different things. PER bit is required by Windows 2008 Failover Cluster devices to enable the persistent reservation data to be saved on the devices. My advise would be not enable PER bit on devices if its not required (there are knowledge base documents on it).

Thanks,

Saurabh

xe2sdc
5 Tungsten

Re: When/Where to use SCSI-3 Flag

M$ cluster is only one of the many OS/clusters that need PER on the volumes... Always refer to the Support Matrix.

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mlee2
3 Argentum

Re: When/Where to use SCSI-3 Flag

Hi Stefano,

Just F.Y.I

The SC3 (SCSI-3) bit can be left enabled.

In simple terms it's function is to specifically respond to any host that asks if the Symmetrix storage device is SCSI-3 compliant. That is, if the Symmetrix is specifically asked "Are you SCSI-3 compliant?" we respond "YES". Otherwise with or without this bit set we are always basic SCSI-3 compliant and will respond to all SCSI-3 protocol commands.The issue arises with some operating systems (like IBM AIX) where the storage is first queried on whether it supports SCSI-3. If the bit is NOT set, and the Symmetrix does not specifically say "YES" we are SCSI-3 compliant, then these operating systems do not send SCSI-3 commands...

The flag is ONLY really required for operating systems (like AIX and I think VMware) where SCSI-3 compliance must be confirmed by the host. But having it set (and never being asked) should never be a problem. That is, these other operating systems continue to treat the Symmetrix as basic SCSI-3 compliant (which it is). Of course, EMC Support always correctly pushes for the "right" flag settings (that is, the EMC QA Engineering certified values). But an "incorrectly" enabled SC3 bit should not be the cause of any issues...

Note that (as highlighted above) the PER bit at the device level is a different matter (and must be set as per the EMC Support Matrix). Similarly for the SPC-2 and OS2007 flags. Nasty things WILL happen if these flags are not correctly enabled (set as per the EMC Support Matrix) on the FA port or at the HBA WWN level. Refer to solution emc219981, this discusses the need for a host reboot when these FA flags are changed.

Best Regards,

Michael.

xe2sdc
5 Tungsten

Re: When/Where to use SCSI-3 Flag

Michael Lee ha scritto:

Note that (as highlighted above) the PER bit at the device level is a different matter (and must be set as per the EMC Support Matrix).

Best Regards,

Michael.

That's what I wanted to highlight... PER bit may be quite dangerous and should be always used only if required by the OS/cluster. And the source of the informations is always the Support Matrix.

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McNally
2 Bronze

Re: When/Where to use SCSI-3 Flag

I'd like to thanks everyone for their comments.  This is exactly what I was thinking, but I wanted to get some outside confirmation.  I am very familiar with and use E-Lab frequesntly, as well as using the host connectivity guides.  Basically it sounds like my configuration is appropriate for my situation, and if needed I will alter the port settings for the odd situations I run into.

0 Kudos
codyhosterman
3 Argentum

Re: When/Where to use SCSI-3 Flag

We are officially making the SC3 bit optional for VMware environments very soon. It is true that turning off the SCSI-3 flag disables ACA handling in the code, but NACA is will be enabled when the SPC-2 flag is enabled (which is definitely required for ESX) so even with configurations as old as ESX 2.5, SCSI-3 should not be needed. But as others said, it won't hurt ESX to be left enabled.

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Cody Hosterman

SVPG Partner Engineering – VMware & Cisco Technologies

Symmetrix & Virtualization Product Group

EMC Corporation

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