This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-users] Shared Storage

TCP offload helps a lot in the case of iSCSI. You get the ability to
send ~60KB of data at once, and your packets are checksummed for free. I
don't actually know what Linux support for RSS is like but if it is any
good you also get automatic distribution of rx workload across multiple
CPU's too, but that only works if you have multiple TCP connections in
flight at once (eg the multiple LUN scenario).

I don't know what iSCSI offload involves... maybe that can help further.

Offload is great, but it's still TCP. The protocol itself is heavy on overhead so your 1gbit pipe ends up being, you know, .8gbit storage and .2gbit protocol (I don't know what the exact numbers are). Offload keeps this away from your CPUs but doesn't do anything on the pipe itself. iSCSI's great when you can't afford FC or FCoE (which still isn't as good as FC) or when you need to do things over a WAN, but it has its cost.


John Madden
Sr UNIX Systems Engineer / Office of Technology
Ivy Tech Community College of Indiana

Xen-users mailing list

<Prev in Thread] Current Thread [Next in Thread>