Fibre Channel (SAN)

Reply
Occasional Contributor
Posts: 19
Registered: ‎03-31-2011

Connections for ISLs

Hi All!

Quick (and dumb) question on my part.

What are the correct cables for ISLs between a 5300 and 300?  I am getting some errors from the ISL ports saying "Severe latency bottleneck detected at slot 0 port 28" which is an ISL port between the two switches.  Wondering if the ISL cables which are up to 10GB are causing it because the SFPs between the Principal and Subordinate switches both have 8GB connections.


Let me know what you think or if there's a better way to figure out what the "Severe latency bottleneck" issue is related to. I did some research and I found that someone had fixed this by either swapping the cables or reducing the connection from 8GB to 4GB.  I'd like to be able to use all of that 16GB of xfer speed instead of dumbing it down to 8GB.


Let me know if you have a quick solution for this one!

Brian

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: Connections for ISLs

Wondering if the ISL cables which are up to 10GB are causing it because  the SFPs between the Principal and Subordinate switches both have 8GB  connections.

This has nothing to do with it. The 10G cables could be rated 10G but only for short distances.

What matters is the :

1) Speed (8G in this case)

2) the distance you're trying to cover

3) type of SFP used

4) what grade (Multimode OM2/3/4 or Singlemode) cable you're using

5) (tied in with 2)) buffer credit allocation

Severe latency bottleneck messages could be running out of buffer credits due to slow drain devices or improper configuration/calculation.

A quick test you could do is to set the speed at 4 or 2 G and watch if the messages dissapear.

Occasional Contributor
Posts: 19
Registered: ‎03-31-2011

Re: Connections for ISLs

In reply:

1) Speed (8G in this case)  - Yes.

2) the distance you're trying to cover - About 10M

3) type of SFP used - 8G to 8G

4) what grade (Multimode OM2/3/4 or Singlemode) cable you're using - This is what I am trying to determine.

5) (tied in with 2)) buffer credit allocation - You may be correct about the buffer credits, but can I change the buffer credits?  These are ISLs.

The operational team is using 10G connector cables (they have patch panels that cover that 10M distance, which I would rather just run the connections through the floor).  I can post later as to what type they are.  In the meantime I will check the credits and then drop it down to 4G to see if that issue goes away.

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: Connections for ISLs

4) what grade (Multimode OM2/3/4 or Singlemode) cable you're using - This is what I am trying to determine.

Ask the or check it yourself, characteristics should be printed on the cable

5) (tied in with 2)) buffer credit allocation - You may be correct about the buffer credits, but can I change the buffer credits?  These are ISLs.

Yes by using the portcfglongdistance command

Super Contributor
Posts: 635
Registered: ‎04-12-2010

Re: Connections for ISLs

Hi Brian,

You should have a look if the performance is very poor on that link. You should check if you have very hight buffer credit zero values.

If you have very poor performance try a link reset to recover your buffers. This will be disruptive.

Please have a look in FOS 7.0 release notes:

Miscellaneous

RASlog message AN-1010 may be seen occasionally indicating ―Severe latency bottleneck detected. Even though it is a ―Warning message, it is likely to be a false alarm and can be ignored.

I hope this helps,

Andreas

Join the Community

Get quick and easy access to valuable resource designed to help you manage your Brocade Network.

vADC is now Pulse Secure
Download FREE NVMe eBook