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RE: [Xen-users] iscsi vs nfs for xen VMs

> Il 26/01/2011 22:24, James Harper ha scritto:
> >>
> >> iSCSI tipically has a quite big overhead due to the protocol, FC,
> >> native infiniband, AoE have very low overhead.
> >>
> >
> > For iSCSI vs AoE, that isn't as true as you might think. TCP offload
> > take care of a lot of the overhead. Any server class network adapter
> > these days should allow you to send 60kb packets to the network
> > and it will take care of the segmentation, while AoE would be
limited to
> > MTU sized packets. With AoE you need to checksum every packet
> > while with iSCSI it is taken care of by the network adapter.
> the overhead is 10% on a gigabit link and when you speak about
> overhead you have mention also the CPU overhead on the storage side.

I don't know the exact size of the iSCSI header, but to be 10% of a
gigabit link it would have to be 900 bytes, and I'm pretty sure it's
much less. If you weren't using jumbo frames then maybe 10% might be
realistic, but that's hardly an enterprise scenario.

> If you check the datasheets of brands like emc you can see that the
> storage platform is sold in iSCSI and FC version ...on the first one
> can use less than half the servers you can use with the last one.
> Every new entry level storage is based on std hardware without any hw
> acceleration ...for example EMC AX storages are simply xeon servers.

Well if EMC are selling workstation grade cards with no TCP offload at
all then I'm not surprised that the performance is so poor.


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