[OpenIndiana-discuss] ZFS remote receive

Roy Sigurd Karlsbakk roy at karlsbakk.net
Wed Oct 31 12:53:11 UTC 2012

> 2012-10-30 19:21, Sebastian Gabler wrote:
> > Whereas that's relative: performance is still at a quite miserable
> > 62
> > MB/s through a gigabit link. Apparently, my environment has room for
> > improvement.
> Does your gigabit ethernet use Jumbo Frames (like 9000 or up to 16KB,
> depending on your NICs, switches and other networking gear) for
> unrouted (L2) storage links? It is said that traditional MTU=1500
> has too many overheads with packet size and preamble delays between
> packets that effectively limit a gigabit to 700-800Mbps...

Erm… That's not true. IPv4 header is 20 bytes. TCP header the same, meaning 40 bytes in total out of 1500 bytes "payload", leaving 1460 bytes left for real payload, or 97.3%. An overhead of 20-30% is *not* correct. The ~3% overhead matches well what I see in practice on my networks. You will get a gain with jumboframes, but mostly lower CPU use for handling the packets, and especially in iSCSI environments, but not much for the lower packet size overhead…

Vennlige hilsener / Best regards

Roy Sigurd Karlsbakk
(+47) 98013356
roy at karlsbakk.net
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