Help with switch Buffers please

[totalnewbie]

Hi Everyone

I’m looking to understand the Priority Queue configuration with regards to Port Buffer usage on HP switches.  We have a SAN environment currently using HP 2910-48G for the ISCI channel and the storage vendor is suggesting Port Buffer might not be suitable.  How is the 6mb shared across the 48 ports – how can we manage its usage and how does this differ on the 7506?

Thanks

[Peter_Debruyne]

Hi,

the 2910 is known to be fairly weak for (intensive) ISCSI usage. The limited buffers cause too many drops, which result in too much tcp retransmits, which can cause a tcp reset under stress conditions.

So some additional buffering will not give you more bandwidth, and it will not make the drops go away, but it will sufficiently decrease the drops so TCP can survive.

*/ The 2910 has support for 8 queues per port, so the buffers are shared over all the ports, and some buffers are reserved for each of these queues. It is typically recommended to set the number of queues to a minimum, so less buffers are waisted as being "reserved" for queues which are never used:

conf

 # default : qos queue-config 8-queues

 qos queue-config 2-queues

 # must reload to activate

 wr m

 reload

*/ The 3500 series have 18MB buffer per group of 24G ports or group of 4 10G ports. So a 3500 48port has a total of 36MB buffer (as opposed to the 6MB for the 2910). This one is highly recommended for iscsi.

*/ The 7500 is a fairly traditional switch, with plenty of network features, but with low packet buffers on the line cards.

On this link:

http://h17007.www1.hp.com/tw/en/products/configurator/index.aspx

You can add a 7500, select a 7506 model, next select I/O slots. Next to the I/O slots, you will see an info icon (i), which gives you this information about buffers and features of the linecards.

Attached screenshot.

So based on the linecards of the 7506, per slot the buffers go from 512K, 2MB, 4MB and 1 type with 128MB.

The 7500 is not the switch to use in case large buffers are required.

If you are looking for new solutions with larger buffers:

* budget friendly : 3500/3800 (procurve line) 18-36MB total

* a bit more : 5920/5830 (comware) 3-3.6GB total

* chassis (much more): 12500 (comware) 256MB per 10G port (about 25MB per Gigabit port)

Best regards,Peter