3750X output drops - SAN/VMware/Iscsi - HELP

[carl_townshend]

Hi all

We seem to be having some issues with some vm / SAN / Iscsi environment, basically running very very slow.

Looking at the switch we are getting output drops on most of these ports, the switch is a 3750X stack

I have checked the port asic stats drop and can see drops in queue 3 on most of the ports of this switch.

mls qos is disabled on this switch.

Is there anything I can do to increase performance and lower the drops on the switch? or do I need to buy a more powerful switch with bigger egress buffers? If so what switch would we be looking at? 3850, or something better?

This is becoming a major issue now so I could do with some help on this ASAP please guys

cheers

Carl

[Leo Laohoo]

We seem to be having some issues with some vm / SAN / Iscsi environment, basically running very very slow.

Looking at the switch we are getting output drops on most of these ports, the switch is a 3750X stack

I have checked the port asic stats drop and can see drops in queue 3 on most of the ports of this switch.

mls qos is disabled on this switch.

Catalyst switches are NOT designed for DC work.  Cisco Nexus series family of switches are designed for DC work because the series have deep buffers suited for SAN-like traffic.

[carl_townshend]

Hi

What is the smallest Nexus switch we can get away with installing for this use? what about the 4900 series ?

what is the difference in the buffer sizes with the nexus and 3750x for example ?

cheers

[Mark Malone]

Hi as its ISCSI you could try enable flow-control on the interfaces if its facing congestion and if your sending jumbo frames the switch needs to have that enabled as well

Do you see any other type of drops in the interfaces ?

As Leo said Nexus would better suit that type of traffic but if you haven't enabled those features it may help

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Yes, by some QoS tuning, you might be able to decrease your port drops.  I'm going to show you what I did for a somewhat similar situation, in response to your question on the 3850 post.  However, I did want to mention that a 3750 has 2 MB of RAM per 24 copper ports or for its uplink ports, so where you connect really busy devices can help or hinder performance.  (I.e. ideally you want to avoid all your busy ports using the same RAM buffer space.)