why do front end director ports WWN does not change after replacement in symmetrix?

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why do front end director ports WWN does not change after replacement in symmetrix?

vmax_fa_all1

 

 

 

This question used to bother me for long time.I used to answer myself like their must be some mechanism EMC is using to get same WWN as old director port to even new director after replacement.Recently I found a primus which helped me to understand deep down on FA WWN.

I will follow the primus emc223285 and try decode Symmetrix WorldWide Names (WWNs) on a VMAX.

We will be using the following WWN as an example: 50000972081349AD

5000097-these hexa numbers are assigned by IEEE and is the vender UID of Symmetrix V-Max.so these
numbers same for any FA WWN of VMAX array.

now let us break down reamaining WWN 2081349AD.
Start by breaking down the hexadecimal digit WWN into binary.

2         0        8        1        3       4        9       A      D
0010 0000 1000 0001 0011 0100 1001 1010 1101

bit35 <—————————————–< bit 0

Starting from left to right, number the bits from 35 on down to 0.

Follow below screenshot along with descritpion to undesrtand well.

bit

 

Bit arrangement description:

Bits 35 through 33:Bits 35 through 33 deal with the build location of the array.  For any given WWN, one of the 3 bits will be set; the other two bits will be not be set.  If bit 35 is set, the array was made in China and the Serial Number starts with CN49xxxxxxx.  If bit 34 is set, the array was made in Europe and the Serial Number starts with CK29xxxxxxx.  Lastly if bit 33 is set, the array was made in the USA and the Serial Number starts with HK19xxxxxxx. In the example provided, bit 33 is set, which indicates the example WWN has a Serial Number starting in HK19xxxxxxx.

Bits 32 through 26:bits 32 through 26, deal with the Symmetrix Model Type.
Refer to the following chart for a breakdown of the bits.

bit 32 26

 

 

 

 

 

In the example WWN, the break down of bits 32 through 26 is 0 0 0 0 0 1 0 which indicates the WWN is HK1926xxxxx.

Bits 25 through 10:Bits 25 through 10 encode the last 5 digits of the Symmetrix Serial Number.  Take those bits and place them into a scientific calculator set to binary, convert the binary into decimal, and you will receive the last 5 digits of the Symmetrix Serial Number.  In the example, bits 26 through 10 come out to be 000 0001 0011 0100 10.  Placing this into a calculator and converting from binary to decimal yields 1234.  If the yield comes out to be a 4-digit number, front pad the number with a 0 to make 5 digits (i.e., 01234). The full Serial Number for the Symmetrix in the example WWN is HK192601234.

binarydecimal

 

 

 

 

 

Bits 9 through 6:  Bits 9 through 6 hold the encoding for the processor letter (CPU letter) for the director.  Use the break out of the bits to the chart below.

bit 9 6

 

Bits 5 through 2: Bits 5 through 2 hold the encoding for the director number for the director.  Use the break out of the bits to the chart below.

bit52

 

the last two bits:Lastly, the last two bits, bits 1 and 0, hold the encoding for the director port.  If the bits are 00, then it is the 0 or A port. If the bits are 01, then it is the 1 or B port.  In the example, it is port 1 or B.

So, finally, WWN 50000972081349AD decodes to VMAX / VMAX 20K HK192601234 director 12g port 1/B 🙂

 

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