Fibre Channel (SAN)

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New Contributor
Posts: 4
Registered: ‎01-19-2012

Severe latency bottleneck detected on ISL / Trunk port

Hello,

could anyone give me a hint how to troubleshoot error "Severe latency bottleneck detected" on ISL/trunk port?

What can cause this problem and how a root cause can be found?

We received this alert on trunk created from two 8Gbit ISL ports between two 5100 switches.

ASAN01:admin> trunkshow -perf

  1:  1->  7 10:00:00:05:1e:36:38:62 100 deskew 15 MASTER

      0->  6 10:00:00:05:1e:36:38:62 100 deskew 24

    Tx: Bandwidth 8.00Gbps, Throughput 37.44Kbps (0.00%)

    Rx: Bandwidth 8.00Gbps, Throughput 51.94Kbps (0.00%)

    Tx+Rx: Bandwidth 16.00Gbps, Throughput 89.38Kbps (0.00%)

  2:  5-> 71 10:00:00:05:1e:36:38:62 100 deskew 16 MASTER

      4-> 70 10:00:00:05:1e:36:38:62 100 deskew 15

    Tx: Bandwidth 8.00Gbps, Throughput 33.12Kbps (0.00%)

    Rx: Bandwidth 8.00Gbps, Throughput 58.08Kbps (0.00%)

    Tx+Rx: Bandwidth 16.00Gbps, Throughput 91.20Kbps (0.00%)

  3: 35-> 35 10:00:00:05:33:ce:61:f5 203 deskew 15 MASTER => trunk with alerts

     39-> 39 10:00:00:05:33:ce:61:f5 203 deskew 16

    Tx: Bandwidth 16.00Gbps, Throughput 442.46Kbps (0.00%)

    Rx: Bandwidth 16.00Gbps, Throughput 433.73Kbps (0.00%)

    Tx+Rx: Bandwidth 32.00Gbps, Throughput 876.19Kbps (0.00%)

porterrshowASAN01:admin> porterrshow

          frames      enc    crc    crc    too    too    bad    enc   disc   link   loss   loss   frjt   fbsy

       tx     rx      in    err    g_eof  shrt   long   eof     out   c3    fail    sync   sig

     =========================================================================================================

35:  374.0m 115.7m   0      0      0      0      0      0      0     70      0      1      2      0      0

39:    3.1g   3.8g   0      2      0      0      0      0      0    204      0      1      2      0      0

Thanks

Radek

New Contributor
Posts: 4
Registered: ‎01-19-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

Here is my alert message:

Time    Level    Message    Service    Number    Count    Message ID    Switch 

Mon Aug 06 2012 20:32:05 CEST    Warning    Severe latency bottleneck detected at slot 0 port 35.    Switch    1241    1    AN-1010    ASAN01 

Looks like buffer credit problem:

Data Center Fabric Resiliency Best Practices:

Bottleneck Detection can detect ports that are blocked due to lost credits and generate special “stuck VC” and “lost

credit” alerts for the E_Port with the lost credits (available in FOS 6.3.1b and later).

Example of a “stuck VC” alert on an E_Port:

2010/03/16-03:40:48, , 21761, FID 128, WARNING, sw0, Severe latency bottleneck detected at slot 0 port 38.

Data Center Bottleneck Detection Best Practices Guide:

<timestamp>, , <sequence-number>,, WARNING, <system-name>, Severe latency bottleneck detected at Slot

<slot number> port <port number within slot number>.

This message identifies the date and time of a credit loss on a link.

The platform and port affected and the number of seconds that triggered the threshold.

ISL is about 500m over multimode shortwawe connection...

Each ISL port is has 26 buffer credits and is configured as L0 for 2km distance...

FOS version on all switches is 6.4.2a.

Any hint how to troubleshoot that?

Occasional Contributor
Posts: 7
Registered: ‎03-08-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

Hi ,

Step 1 -- Check which end device connected to edge switch port utilising more .

Step 2 -- Add one more port for trunking and try to increase buffer credits as well .Monitor for sometime .

Step 3 -- This is happening only on certain time period ,check any backup is running .

Above hint may be helpful i guess.

New Contributor
Posts: 4
Registered: ‎01-19-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

Hi,

Step 1 -- Check which end device connected to edge switch port utilising more .

OK, but is it really relevant if I have enough bandwidth in trunk for high-utilizing device?

Step 2 -- Add one more port for trunking and try to increase buffer credits as well .Monitor for sometime .

trunk is made from two 8Gbit/s ISL ports and is never utilized up to 100%

Step 3 -- This is happening only on certain time period ,check any backup is running .

Yes, it's related to time when backups are running but any port is not utilized so much and trunk utilization is low.

Occasional Contributor
Posts: 7
Registered: ‎03-08-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

Hi ,

Then problem will be on buffer credits value only it seems.Since a device experiencing latencies more slowly than expected means buffer credits does not returned and load is high too .This is mentioned in fabric resiliency best practice . I am unable to attach that document since option not available .Share your mail id if you don't have that document.

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: Severe latency bottleneck detected on ISL / Trunk port

Check if, on any other F-port in these switchs, there are frame discards. Because if there are no stuck VC in the ISL, there could be a slow drain device causing the issue.

New Contributor
Posts: 4
Registered: ‎01-19-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

Problem is solved.

Root cause of this problem has been one erroneous port on second switch with id 203.

BSAN01:admin> porterrshow

frames      enc crc    crc    too    too bad    enc disc   link   loss   loss frjt   fbsy

tx     rx in    err    g_eof  shrt long   eof     out   c3 fail    sync   sig

=========================================================================================================

28: 0      0 0      0 0      0 0      0     13.9k   0 0      0 0      0      0

SFP has been identified as a failing item in fabric. After its replacement problem is gone.

Radek's IT Blog: Severe latency bottleneck detected on ISL / Trunk port

Radek

Occasional Contributor
Posts: 9
Registered: ‎08-03-2012

Re: Severe latency bottleneck detected on ISL / Trunk port

We are having the same issue - the port is trunk port ( 8GB 5100) .

, 372, FID 128, WARNING, switch , Severe latency bottleneck detected at slot 0 port 23.

the answer above is not clear ? I see the traffic flowing fine on both sides of the trunk - upstream and downstream but I am having all these bottleneck error , our application keeps complaining about timeouts , slow storage and bad cable ?

The cable if long distance going from port 23 to patch panel , to fiber termination box and it connects to another down stream switch about 1/4 mile via dark fiber.

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