We have a pair of Nexus 5596T but when configured fro a no-drop class of 9216 MTU, the default ingress buffer is 90k. The max is 152k
We are running only iSCSI for Dell EQ. We bought Nexus 9k based on buffer size but found the 9k max buffer is less. TX pause frames abound and iSCSI disconnects seem to happen. Given no buffer monitoron 5596T, we are thinking we are out of buffers.
Based on the below;
A) Is there a Cisco switch that supports large buffers in a no-drop class?
B) If the max buffers is 152000 bytes and the maximum pause-threshold value is 103360 bytes, how do the buffers between 152000 and 103360 get used?
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Table 1 Cisco Nexus 5500 Platform Default Buffer Allocations Per Port
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Traffic Class
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Ingress Buffer (KB)
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Class-fcoe
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79.360
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User-defined no-drop with an MTU less than 2240
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79.360
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User-defined no-drop class with an MTU greater than 2240
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90.204
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Tail drop traffic class
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22.720
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Class-default
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All of the remaining buffer (470 with default QoS configuration)
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Specifies the buffer threshold settings for pause and resume for 3000m lossless Ethernet:
- buffer-size—Buffer size for ingress traffic, in bytes. Valid values are from 10240 to 490880.
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Note
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On a Cisco Nexus 5020 switch, you can configure a maximum buffer size of 143680 bytes.
On a Cisco Nexus 5500 Series device, you can configure a maximum buffer size of 152000 bytes.
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We bought a 9k and the same applies although the max buffer value is less.
buffer threshold settings for pause and resume.
- buffer-size buffer-size—Specifies the buffer size for ingress traffic, in bytes. Valid values are from 10240 to 490880.
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Note
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You can configure a maximum buffer size of 143680 bytes.
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- pause-threshold xoff-size—Specifies the buffer limit at which the port pauses the peer, in bytes. Valid values are from 0 to 490880.
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Note
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You can configure a maximum pause threshold value of 58860 bytes.
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- resume-threshold xon-size—Specifies the buffer limit at which the port resumes the peer, in bytes. Valid values are from 0 to 490880.
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Note
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You can configure a maximum resume threshold value of 38400 bytes.
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- pfc-cos cos-value—Specifies the CoS values on which to assert PFC. Valid values are from 0 to 7.
