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

On Wed, Jan 26, 2011 at 11:10:12PM +0100, Christian Zoffoli wrote:
> Il 26/01/2011 22:24, James Harper ha scritto:
> >>
> >> iSCSI tipically has a quite big overhead due to the protocol, FC, SAS,
> >> native infiniband, AoE have very low overhead.
> >>
> > 
> > For iSCSI vs AoE, that isn't as true as you might think. TCP offload can
> > 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 adapter
> > 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 yourself
> > 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 resources
> overhead you have mention also the CPU overhead on the storage side.
> If you check the datasheets of brands like emc you can see that the same
> storage platform is sold in iSCSI and FC version ...on the first one you
> can use less than half the servers you can use with the last one.

This is mostly because of:
        - EMC's crappy iSCSI implementation.
        - EMC wants to sell you legacy FC stuff they've invested a lot in.

See dedicated iSCSI enterprise storage like Equallogic.. the way it's meant to 

Microsoft and Intel had some press releases around one year ago
demonstrating over one *million* IOPS using a single 10gbit Intel NIC,
on a *single* x86 box, using *software* iSCSI.

> Every new entry level storage is based on std hardware without any hw
> acceleration ...for example EMC AX storages are simply xeon servers.

Many of the highend enterprise storage boxes are just normal (x86) hardware.
Check for example NetApp.

The magic is all in *software*.

-- Pasi

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