[OpenIndiana-discuss] ISCSI SSD Performance

[Richard Elling]

On Feb 16, 2013, at 3:59 PM, Sašo Kiselkov <skiselkov.ml at gmail.com> wrote:

> On 02/17/2013 12:52 AM, Grant Albitz wrote:
>> Yes jim I actually used something similar to enable the 9000 mtu that's why I want familiar with the config file method.
>> 
>> dladm set-linkprop -p mtu=9000 InterfaceName
>> 
>> 
>> Flowcontrol is currently off on the zfs host but enabled by default on esxi,
> 
> This actually could be it - iSCSI uses TCP and if the ESXi host is
> having trouble keeping up, it might be trying to get the OI host to slow
> down by sending it TX pause frames. If the OI host ignores them and
> continues firing iSCSI packets at full, the ESXi host will drop some of
> them, which will trigger TCP's retransmission - this introduces latency
> bubbles and significant performance penalties (even mild packet drop can
> wreck havoc on a TCP link's throughput).

Flow control is logged in kstats for most NICs (kstat -n statistics)
Unfortunately, there is no consistent statistic name across NIC drivers.
For example, e1000g uses statistics XOFFs_Xmitd and XOFFs_Recvd to
count flow control packets.
 -- richard

> 
> Cheers,
> --
> Saso
> 
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-- 

ZFS storage and performance consulting at http://www.RichardElling.com