Fibre Channel (SAN)

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Contributor
Posts: 35
Registered: ‎01-05-2005

E-port buffer credit

Hi all,

I have an IBM blade chassis switch model 5070 (8Gbs) without trunking E-ports.  I noticed the buffer credits on those E-port is only 17 each from the result of portbuffershow command.  This seems low for an 8Gbs switch. does anyone know what the default buffer-credit allocation (not long distance, 2Km) should be on this switch?  Thanks in advance.

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

Re: E-port buffer credit

Typically an port in L0 mode (default) wil get around 20 credits or so. At 8 G this amounts to a distance of 1KM (in credits) with full payload frames.

Cable specification @ 8G for OM3 150M and OM4 190M.

I think your save with 17 credits, but it all depends on the payload.

Regular Contributor
Posts: 201
Registered: ‎11-24-2009

Re: E-port buffer credit

Hi SANuser,

for a 2-km link LE mode is preferred. This mode will allocate 46 credits to the E-port which is enough for up to 10 km at 8 Gbps.

You'll also need single-mode cabling and longwave SFPs if you exceed distances mentioned by dion.v.d.c above.

Hope this helps,

Linar

Contributor
Posts: 35
Registered: ‎01-05-2005

Re: E-port buffer credit

according to the admin guide (v6.x), specify LE mode to configure E-port of distance Greater than 5km and up to 10km.

Contributor
Posts: 35
Registered: ‎01-05-2005

Re: E-port buffer credit

Yes, in L0 mode, which is the default, according to the admin guide, a total of 20 buffers are reserved for data traffic + overhead so I should at least get 26 total regardless of speed.  again, not sure why I got only 17 for my E-port without any changes to the default port settings.

thanks,

Regular Contributor
Posts: 201
Registered: ‎11-24-2009

Re: E-port buffer credit

Like dion.v.d.c said, L0 mode allocates a fixed amount of credits (20) which is not good enough for a 2-km link at 8 Gbps. For this reason LE mode is preferred in that situation.

I believe 17 buffers is the default for embedded platforms. A 8/24c blade switch in my lab reports 17 buffers as well.

Hope this helps,

Linar

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

Re: E-port buffer credit

@ SANuser

I have some questions.

-What distance are you trying to cover or round trip times are you getting

-At which speeds do you want to do this.

-What is the guestimated payload size per frame

Answer those if you will.

Based on those figures it possible te calulate how much buffers are needed.

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