IOM12 and IOM6 mixed stack path throughput

[pedro_rocha]

Hi,

When we have a stack with both IOM6 and IOM12 (maintaining one speed transition, as supported), does the paths to both beginning and end of the stack goes 6Gbps? Or it will have one side 12Gbps and the other 6Gbps?

Regards,

Pedro

[Ontapforrum]

Good one, I read this article and found it very useful. If I followed (article) it correctly, it appears that one-end will be 6 and other 12, maintaining a single transition. I guess considering it is 6-6-12, or 6-6-12-12, but not 6-6-12-6 or 12-12-6-12. Hopefully, what I am assuming is correct but cannot be 100% sure.

https://docs.netapp.com/us-en/ontap-systems/sas3/iom12-hot-add-mix.html#cable-shelves-for-a-hot-add

[pedro_rocha]

Hi, yeah.. I also saw that. It's not clear from the text...

[SpindleNinja · Accepted solution]

I went to check on a system that is A300 -> DS2246 (IOM6) -> DS224c (IOM12) -> A300

Looking at "expander_phy_state" you can see the state of the drives - 
There's a  physical (physical connection) and logical (data rates) rates.  

(Logical rate is the lowest common rate of all links.)

Drives in the DS224c look like ->  "12.0 Gb/s(6.0)"

Drives in the DS2246 look like -> "6.0 Gb/s"

Looking at the connection from DS2246 IOMA Circle to DS224c IOMA (p1) to DS224c IOMA (p3)back to the controller it looks like this -> 

0/P0:0 6.0 Gb/s          --- --- --- --- 0      0      0      1      0      1      ----------------
 1/P0:1 6.0 Gb/s          --- --- --- --- 0      0      0      0      0      1      ----------------
 2/P0:2 6.0 Gb/s          --- --- --- --- 0      0      0      1      0      1      ----------------
 3/P0:3 6.0 Gb/s          --- --- --- --- 0      0      0      0      0      1      ----------------

 8/P2:0 12.0 Gb/s         --- --- --- --- 0      0      0      0      0      1      ----------------
 9/P2:1 12.0 Gb/s         --- --- --- --- 0      0      0      0      0      1      ----------------
10/P2:2 12.0 Gb/s         --- --- --- --- 0      0      0      0      0      1      ----------------
11/P2:3 12.0 Gb/s         --- --- --- --- 0      0      0      0      0      1      ----------------   

TLDR -

The stacks runs at the lowest common speed.

SAS3 to SAS3 runs at 12 

SAS2 to SAS3 runs at 6 

If you upgrade the DS2246s to DS2246-12 the stack will run at 12, while the backplane of the DS2246 remains at 6. 

As far as helping make the doc more clear. What do you think would help?  something related to Drive and stack speed while in a mixed SAS2-SAS3 stack?   

[pedro_rocha]

Hi,

Thanks for the answer.

As far as for the doc improvement, I guess that having the words "The stacks runs at the lowest common speed" is sufficient.

Pedro

"

[JonathanGaudette]

One side will be 6gbit and one side with be 12gbit. If you had 6gbit at both ends, it would be two "speed transitions" and be considered incorrect.

[Amador]

I think we can cover this with How to cable an IOM12E platform with IOM6 and IOM12 storage shelves in Multi-Path HA - NetApp Knowledge Base