Note to self: check for gigabit Ethernet
One thing I should remember is that before I start measuring things like iSCSI performance, I should check to make sure that I'm actually using a gigabit Ethernet connection. Conversely, if I get unexpectedly terrible high-level performance, perhaps I should make a point of immediately checking the network speed. Especially if the terrible performance is around 10 megabytes a second.
(This is especially embarrassing when I forget this for the second time.)
This can happen to us for a combination of two reasons; first, we don't have a switch in each rack, and second, we still have a mix of gigabit and 100 megabit switches in our machine room. This makes it easy to have accidents and omissions when one drags cable around for new machines, including the ever-popular game of 'which of these two identical cables is gigabit and which is only 100-mbit?'
(One of the morals of that game is to label the cables before you start running them under the floor.)
I think we may now have enough gigabit switches that the sensible thing to do might be to rip out all of the 100 mbit switches that are on (currently) mixed networks and replace them with gigabit switches. At the very least we could do this for all of the networks that we use in the machine room.
(There are some networks that are 100 mbit only and are almost certainly going to stay that way, generally because they have a high wiring density.)
Sidebar: on the naming of speeds
On a side note, I have to say that '100 megabit' networking really could do with a less awkward label. Gigabit Ethernet has, well, 'gigabit' and 10 gigabit Ethernet is commonly '10G', but all of '100 megabit', '100-mbit', '100 Mbps', and '100M' read oddly to me, and '100TX' feels too obscure.
(Plus, if we are being really obscure, Wikipedia tells me that there are several 100 megabit over copper standards, not just 100BASE-TX, although the alternatives have pretty much died out.)