Thin Client and Virtual Machines Thread, Xenserver and jumbo frames in Technical; It seems that Xenserver doesn't support jumbo frames, it certainly doesn't upto version 5 according to a citrix engineer on ...
20th July 2009, 09:14 PM #1
Xenserver and jumbo frames
It seems that Xenserver doesn't support jumbo frames, it certainly doesn't upto version 5 according to a citrix engineer on the forum. I can only find one reference to jumbo frames in the 5.5 admin guide which suggests that you can set it but i've found one post suggesting that it doesn't work and there's no mention of it on the citrix forum.
As my Sun SAN and HP switches support them it seems a shame that Xen doesn't.
Does anyone know different?
20th July 2009, 10:15 PM #2
@cookie_monster: If you're using NFS, I think that jumbo frames becomes less relevant. The Sun iSCSI stack isn't as good as NFS either so NFS is surely the way to go?
21st July 2009, 08:33 AM #3
Yes a good point I'm going to look into NFS today I realised that I can created a virtual disk in Xen and present it to a windows host which then will just see it as a D: drive. This will allow me to use FSRM without needing to map an iSCSI LUN with the Windows iSCSI initiator.
That's one reason why I was avoiding NFS to start with I'll have a play with NFS later. Any recommendations for setting up NFS for hosting VM's, I was told to carve iSCSI LUNS into multiple 250Gb partitions and no bigger as it reduces performance, any caveats like this with NFS?
I'll have to have a read up on NFS and frame sizes are jumbo frames less necssary as it's not sending out data that's been formated in NTFS cluster sizes? I've read so often that block level storage is way faster than file based that I just assumed iSCSI would be faster.
This makes interesting reading
Network File System (NFS) transfers data in 8,192-byte blocks. So adding room for headers, an attractive maximum Ethernet frame size for NFS applications is 9,000 bytes.
So jumbo frame support could be usefull anyway once Xen supports it.
Last edited by cookie_monster; 21st July 2009 at 09:12 AM.
21st July 2009, 09:58 AM #4
BTW... see page 183 of the XenServer 5.5 Admin Guide:
Is your box in production yet? If not, could you perform a performance copmparison between iSCSI, iSCSI with jumbo frames, NFS and NFS with jumbo frames?
Maximum Transmission Unit of the VIF in bytes. This parameter is read-only, but you can override the MTU setting with the mtu key using the other-config map parameter.
For example, to reset the MTU on a virtual NIC to use jumbo frames:
xe vif-param-set \
21st July 2009, 10:48 AM #5
I had seen that section in the admin guide but there's very little info on it and I did see one post online about it causing a race condition on startup so I was being cautious.
If I get time I’ll run a comparison but it’s getting a bit frantic at the moment so I’m not sure I’ll get chance.
Do you use something like IOMeter for this?
Last edited by cookie_monster; 21st July 2009 at 10:53 AM.
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