Rule 17

Ya, thats right. But EMC says in DMX (Direct matrix architecture) each FE is connected to each other BE.

Then why this Rule 17 come into picture. Whats the logic behind this rule.

"Rule 17" is used on Symmetrix/DMX to ensure that when you connect a host, FAs that it's connected to reside in different power zones on the frame. For example when i would zone a host to DMX3/DMX4 i would always select two FAs that add up to 17, ie: 8A0 and 9A0 or 7C1 and 10C1.

the only reasoning i heard was about redundant power zones.

This discussion has gone on in various threads of various forums here a few times. While the "old timers" may tend to tell you that you still need to follow the Rule of 17, the reality is that in recent years on the newer equipment DMX3 and VMax for sure, and I'm not sure how much further back though) this is no longer a rule.

So, does it still make sense? If you want to simplify troubleshooting and keep everything neat and tidy then it does make sense as a general best practice, but it does not provide any special advantages over several other ways of configuring things. It does have the advantage of still being a valid configuration though, and it is well understood and easy to remember. I can't help but notice that the VMax design still allows for following the rule if you have the right configuration and want to.

On that note, we do still follow the Rule of 17 for our DMX3 arrays, but not for our new VMax. It was a concious decsion on our part because we can only continue to follow it "religiously" if we always add engines in pairs (which we may or may not do).

RULE-17,

which shows that there is Redundancy of the devices from the FA ports. If one of FA when down, still the host can see the provisioned Devices from the other FA port. In the same way we can see redundancy on switch side(Fabric-A and Fabric-B) and also on Host Side(HBA1 and HBA2);

If HBA1 fails the host will receive alert that devices are having only single path.

Rule-17 means sum of FA directors pairs must be 17. As if { 1-16, 2-15, 3-14, 4-13, 5-12, 6-11, 7-10, 8-9}

If anyone knows of any documents, white paper or article on how rule 17 is implemented in VMAX then I would be grateful. I am curious to know how rule 17 is implememted on VMAX.

Hello,

I am moving this discussion to the EMC Support forums, where it will be answered by our experts shortly.

Thank you,

Tarini

Rule of 17 came into play long ago back in the age of the Symm3.  The Symm3 was a bus based system with an odd and even bus.  If termination was lost then the bus would go down affecting either the odd or the even bus.  The rule of 17 ensured that a host would have a connection on both the even and the odd bus so it would not lose all of its pathing.  This rule has been carried forward into the rest of the line of Symmetrix arrays.  It no longer applies once the direct matrix came into play; although if possible to follow it its not a bad idea to do so.

we don't have rule of 17 in vmax box now. For example, the first vmax engine we add would be engine 4, which is director 7 and director 8. It won't make up a rule 17 in any way