How to Change MTU Size in Exadata Environment
(Doc ID 1586212.1)
Last updated on DECEMBER 09, 2018
Applies to:Exadata X3-8 Hardware - Version All Versions and later
Oracle Exadata Hardware - Version 184.108.40.206 and later
Oracle Exadata Storage Server Software - Version 220.127.116.11.2 to 18.104.22.168.1 [Release 11.2]
Exadata Database Machine X2-2 Hardware - Version All Versions and later
Exadata Database Machine V2 - Version All Versions and later
Having a larger value for MTU such as 65520 bytes = 64kb will require more memory pages to support IPoIB, the large frame size is derived from HCA IB Card with driver support at the o/s level. In some cases it may be required to reduce the size of the frame to avoid memory page fragmentation issues.
Value of 65520 bytes would require 18 contiguous memory pages based on a default kernel pagesize.
IP over IB similar to TCP on Ethernet does contain additional packet overhead.
| Infiniband Header | IPoIB Header | IP DATA |
Lets assume the kernel by default will use a pagesize of 4k, you can verify this value -->
For more in-depth analysis slabinfo can be used.
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