[ Date Index ] [ Thread Index ] [ <= Previous by date / thread ] [ Next by date / thread => ]
On Sun, 16 May 2010, Simon Waters wrote:
Rob Beard wrote:On 16/05/10 08:54, Simon Waters wrote: I managed to swap that out with a Gigabit switch and it seems much faster although not the full 1GBit (250MBit, so it's still a lot better than the couple of Megabits it was running at).How do you measure 250Mbps? Few things can use Gbps Ethernet to the full without tweaking. If you are getting more than 100Mbps than the gigabit Ethernet is probably working as designed. I did some benchmarking using some new kits at work a while back, and I could get good speeds over a single FTP connection but no where near 1Gbps. Using SMB protocol connections with lots of small files (i.e. what we actually use the boxes for), the numbers were depressingly low but they just reflects a chatty protocol with lots of round trips and other overhead.
Indeed!A lot of the early kit couldn't handle Gb speeds very well at all, and there is a lot of tuning to do - both at the hardware/driver level and the higher layers - e.g. your typical disk has a head bandwidth of between 50-80Mb/sec - which is less than Gb running flat-out... You need expensive disks (10-15Krpm, or the WDC dual-head ones) or a very highly tuned RAID array - with fast disks and interconnect to saturate Gb Ethernet to/from disks.
And remember your PCI bus is only 133MB/sec (although it can go faster is posh servers :) - so a server with one PCI bus with both the disks and Ethernet on the same bus will struggle to keep up. PCIe is the way to go...
(fastest array I built for a client could sustain writes at 250MB/sec, but it cost £14K at the time )-:
And even Linux isn't always the best - well, not out of the box. There are still a few tunable parameters you can fiddle with - enabling jumbo frames for a start (on win too), but make sure the switches can cope!
For throughput monitoring I've used iperf in the past - it's very flexible and there is Windows as well a Linux support for it - but it's not just about raw network speeds - server efficiency (or lack of it) will render even the most expensive switches useless!
Gordon
-- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html