Our ESXi 6.7 iSCSI vmkernel interfaces are set up with an MTU of 1500. I understand they should be set with MTU up to 9000 bytes.
Can I safely change the value from 1500 to 9000 during production or under which circumstances can I do the change?
Thanks for comments and tips
best regards Tor
> I understand they should be set with MTU up to 9000 bytes.
Apparently you read obscure advice from obscure sources.
Changing the MTU to jumbo-frame size only makes sense if your complete iSCSI environment also uses the same non-default value.
Just changing the MTU because some idiot said so in a blog is a recipe for desaster ( poor performance )
Jumbo frames made a lot of sense back in the days when CPUs were slow compared to CPUs nowadays.
Nowadays the performance gain you could EVENTALLY get with jumbo-frames hardly justifies the higher risk of running misconfigured setups.
You consider doing such a switch during production ??? - 10 points for warrior-attitude - 0 points for use of common sense
... and how many points for asking for advice before even considering touching my setup...?
Does your storage use Jumbo-frames ?
If yes - which MTU is configured ?
>>> Can I safely change the value from 1500 to 9000 during production ...
Short answer: No!
Setting MTU sizes must be done end-to-end , i.e. on the storage ports, the physical switch ports, the virtual switch(es), and the virtual port group(s). Setting it only on one end will result in traffic loss, which also means that if you change the MTU on the storage systems, all your hosts may be affected. For such a modification you need to plan downtime.
Whether and how much you will benefit from a larger MTU size depends on e.g. the network speed, storage vendor recommendations, etc. Often other settings like delayedAck, or iops will improve the performance more than simply configuring Jumbo Frames.
What Storage System (Vendor/Model) do you use? Does the vendor provide Best Practices for that model?
Thanks a lot for a VERY informative answer. I will checkout my storage vendor's recommendations and I have pleanty of weekends to plan downtime.