09-15-2011 12:17 PM
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.
09-15-2011 01:05 PM
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.
09-16-2011 02:23 AM
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,
09-16-2011 06:05 AM
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.
09-16-2011 06:28 AM
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,
09-16-2011 07:35 AM
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.