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Regular Contributor
Posts: 178
Registered: ‎04-21-2008

Question about F-Port buffers

Hi all -

I discovered new CLI since 6.2.2, portcfgfportbuffers and portbuffershow.

With portbuffershow, I understand I have lots of buffers available for port groups :

besw32:admin> portbuffershow
User     Port     Lx           Max/Resv    Buffer Needed          Link   Remaining
Port     Type    Mode          Buffers     Usage  Buffers     Distance  Buffers
----     ----    ----          -------     ------ -------     --------- ----------
  0        E        -            8         17         17             3km
  1        F        -            8          8          -             -
  2        F        -            8          8          -             -
  3        F        -            8          8          -             -
  4        F        -            8          8          -             -
  5        F        -            8          8          -             -
  6        F        -            8          8          -             -
  7                 -            8          0          -             -
  8        G        -            8         17          -             -
  8        F        -            8         17          -             -
10                 -            8          0          -             -
11                 -            8          0          -             -
12                 -            8          0          -             -
13                 -            8          0          -             -
14                 -            8          0          -             -
15                 -            8          0          -             -
16                 -            8          0          -             -
17                 -            8          0          -             -
18                 -            8          0          -             -
19                 -            8          0          -             -
20                 -            8          0          -             -
21                 -            8          0          -             -
22                 -            8          0          -             -
23                 -            8          0          -             -          457
----------------------------------------------------------------------------------
Here 457 available buffers ...
I'm able to increase buffer credit on any F-port (for instance port 1) :

besw32:admin> portcfgfportbuffers --enable 1 24

Success.

besw32:admin> portbuffershow

User     Port     Lx           Max/Resv    Buffer Needed          Link   Remaining

Port     Type    Mode          Buffers     Usage  Buffers     Distance  Buffers

----     ----    ----          -------     ------ -------     --------- ----------

  0    E   -   8     17     17    3km

  1    F   - 24     24      -    -

  2    F   -   8      8      -    -

  3    F   -   8      8      -    -

  4    F   -   8      8      -    -

  5    F   -   8      8      -    -

  6    F   -   8      8      -    -

  7        -   8      0      -    -

  8    G   -   8     17      -    -

  8    F   -   8     17      -    -

10        -   8      0      -    -

11        -   8      0      -    -

12        -   8      0      -    -

13        -   8      0      -    -

14        -   8      0      -    -

15        -   8      0      -    -

16        -   8      0      -    -

17        -   8      0      -    -

18        -   8      0      -    -

19        -   8      0      -    -

20        -   8      0      -    -

21        -   8      0      -    -

22        -   8      0      -    -

23        -   8      0      -    -     441

----------------------------------------------------------------------------------

and see 441 (457 - 16 added to port 1) available buffers.
Does it make sense to increase buffers on overloaded F-ports (high tim64_txcrd_z under portstats64show) ?
Kind regards
--
david

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

Re: Question about F-Port buffers

Hello David,

you have raised an interesting question.

The command reference guide explain the counter tim64_txcrd_z as followed: 

Number of times that the TX BB_credit was at zero.

This means that the switch transport side is waiting for the device which is connected to that port. If you increase the number of buffers it will increase your problem on the connected device. If the counter increase on a F-Port this means that the switch ports has send 8 data frames out and has not received any receiver-ready message back for more than 2.5us. The device is processing and have no time for IO requests currently.

If I understand the thinks correct the switch and device (other switch as well in case of an ISL) negotiate the numbers of buffers which can be used for data transfer. This means both sides need to be capable to use more buffers. Buffers mean in general memory per port to store data which have to be send. Not all HBA have the same number of memory on board.

Primary I would only increase the number buffers for ISLs with a distance of more than 6km. Extended Fabric lic is needed if you would like to run links over 10km full utilized. Full utilized means if your frames are mainly full.

I hope this helps.

Best regards,

Andreas

Regular Contributor
Posts: 178
Registered: ‎04-21-2008

Re: Question about F-Port buffers

Hi Andreas,

thanks a lot for your answer, I don't think I will increase buffer on slow F-Ports

Kind regards,

--

david

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