Fibre Channel (SAN)

Reply
Frequent Contributor
Posts: 76
Registered: ‎02-13-2010

ISL buffers

I have two Brocade 300 switches connected by one ISL set to L0. The distance between them is about 100 mts. I was wondering if the buffer credits are enough because Max/Resv  Buffers = 8 and Needed Buffers = 17.

1. Does it mean that I need more buffers?

I also tryed setting long distance to LE and now Max Buffers = Needed Buffers = 46.

2. What option is better?

# portbuffershow

User     Port     Lx           Max/Resv    Buffer Needed          Link   Remaining
Port     Type    Mode          Buffers     Usage  Buffers     Distance  Buffers
----     ----    ----          -------     ------ -------     --------- ----------
  7        E      -               8         17      17            <2km

# portcfglongdistance 7 LE

# portbuffershow

User     Port     Lx           Max/Resv    Buffer Needed          Link   Remaining
Port     Type    Mode          Buffers     Usage  Buffers     Distance  Buffers
----     ----    ----          -------     ------ -------     --------- ----------
  7        E      -               46         46      46            10km

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

Re: ISL buffers

1)  Based on the output i wouldn't worry about it as it seems you missed the colomn titled "Buffer Usage" with value 17 which is the same as the one titled "Needed Buffers".

But if you want to know it depends, calculation of buffers is done based on distance speed and payload.

buffer credits = ( *  * 1000)/payload size

To get the payload size,we actually use average frame size, which is a bit inaccurate but easier

First reset the portcounters as they could have rolled over.

Then wait for an hour or so or whenever you feel like you got a good sample set, but make sure the couter don't roll over or else the numbers are worthless.

Do a portstats64show -long (which I prefer as it takes longer for counters to roll over, but portstatsshow is fine) and do

( / ) * 4 = average bytes per frame ~ equals average payload

A 100 meter link the default L0 should be fine unless you have an exceptional small payload per frame.

At 8G a full frame doesn't even fit as its spans nearly 500 meters

Do you get bottleneckmon warnings against the ISL ports?

2) That depends on 1)

added formula

Frequent Contributor
Posts: 76
Registered: ‎02-13-2010

Re: ISL buffers

There is no error in the log. I was just worried based on the output of portbuffershow because I don't know why the Maximum Resv Buffers is 8 but the Used buffers can go anyway higher up to 17.

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