Web Hosting Talk : Web Hosting Main Forums : Cloud Hosting : MTU size for onAPP connected to SAN

[WebGuyz]

Anybody out there running onapp I was curious what your MTU size if for the eth nic's talking to your SAN. Are you using Jumbo Frames with a larger MTU size around 9000 or what?

Thanks!

[CRego3D]

Yes, definitely use jumbo frames @ 9000 (actually, you have to), we have in some cases seen some clients use a smaller MTU, but 9000 is the advisable rate.

[WebGuyz]

Ran into a situation where I had a working onapp service but had a SAN problem. Was having all kinds of connection problems after my SAN was back up using an MTU of 9000. Turned out the cause was a switch setting that I changed after a recommendation by the san engineer. Turns out if you want jumbo frames on a dell 6248 you have to set the ports MTU to 9216, if you set them to 9000 as was recommended it will cause havoc. I should never have changed them but I think I got it sorted now. My HV's are being set to MTU is now 9000 and working fine.

Thanks!

[CRego3D]

Originally Posted by WebGuyz

Ran into a situation where I had a working onapp service but had a SAN problem. Was having all kinds of connection problems after my SAN was back up using an MTU of 9000. Turned out the cause was a switch setting that I changed after a recommendation by the san engineer. Turns out if you want jumbo frames on a dell 6248 you have to set the ports MTU to 9216, if you set them to 9000 as was recommended it will cause havoc. I should never have changed them but I think I got it sorted now. My HV's are being set to MTU is now 9000 and working fine.

Thanks!

Excellent tip to be aware of, glad to see it's sorted for you now

[Uncorrupted-Michael]

The same goes for the PowerConnect 5448 switches from Dell.

[(Stephen)]

I would guess this is because you have them on specific VLANs?

I've encountered this issue in working with switches on cross brand networks before, as some switches do the 9000 as the total max MTU, and some count the extra vlan headers and encapsulation and allow a bit over 9000 to properly pass the packet, but data load still at 9000.

We can across this specifically when working with some alcatel gear one provider utilized.