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Re: [Xen-users] Shared Storage

On Apr 26, 2011, at 5:47 PM, John Madden wrote:

On 04/26/2011 04:31 PM, Javier Guerra Giraldez wrote:
On Tue, Apr 26, 2011 at 3:21 PM, Jonathan Tripathy<jonnyt@xxxxxxxxxxx> wrote:
On 26/04/2011 18:53, Javier Guerra Giraldez wrote:
more like .96gbit storage and .04gbit protocol.... or .993/.007 on jumbo

Are you using TCP and/or iSCSI offload in your NIC? Those seem like pretty
good numbers.

that's the protocol overhead; what John guessed would be .8/.2   He's
right in that no amount of offloading or CPU power would improve on
that, but his numbers are way off.

Some good summary numbers are near the bottom here (PDF):


With a MTU of 1500, they're claiming 94.93% payload. On GbE, I don't believe I've seen more than ~100MB/s on any protocol, hence my estimate of 20% overhead.


In sequential writes I get nearly all the 125MB/s using iSCSI on BCM5709 without the iSCSI Offload module enabled (better yet, module is loaded but reporting my cards do not support it, although they do).

It fluctuates from normally 120MB/s to rarely 125MB/s.

The switch my servers are connected to, also contains an iSCSI Offload engine which is enabled, but I don't know the details about that (I don't even understand why would the switch care about the iSCSI payload in the first place)... However, that might be the reason to get literally 125MB/s at times.

Best regards,

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