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I have a Nextenta box connected to another Windows 7 machine via iSCSI. It is getting horribly slow average write speeds, but a large active time in the Windows Resource Monitor.

The machines are connected via a cross over cable, so I don't think it's related to network bandwidth. A screenshot of the problem is here:

What steps can I take to diagnose this?

More Information

Unfortunately this is in a completely remote installation (a remote mining town on the other side of the country - Australia). The people onsite aren't technically literate to swap cables and other tasks. Sending a technician is an option we don't want to use unless we have too. Although I do appreciate it may not be resolvable unless in person.

My reason for assuming that it's not a network issue is due to the fact that it's a crossover cable, which can reliably ping the Nextenta box. There is no packet loss and the response is sub 1ms (even when the slow transfers are occurring in the linked screenshot). So I don't believe (but can't guarantee) that the cable is the issue.

I don't necessarily think that the issue is due to Nextenta. My first assumption is that it may be due to iSCSI in general. As in, maybe there are some obscure Windows settings I need to set to make iSCSI run at a reasonable speed. Browsing the web interface of Nextenta is fast and reliable, again leading me to believe that it's an iSCSI protocol issue.

The intention of using Nextenta in the question was hopefully that someone would reply with "Yeah there is a strange bug with Nextenta version XYZ". However I do think the problem is related to iSCSI (or Nextenta's implementation). What methods can I use for diagnosing poor iSCSI performance?

I apologise for the lack of information in the original question.

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The problem with assuming it is nexenta is that the perforamnce is not BAD - it is pathetic. I would expect even a bottleneck to only occur about 10 tiems the speed unless you hit it with a lot of parallel requests. This is NOT a "windows iscsi setting" at this patheticl level. – TomTom Feb 10 '12 at 11:55

A lot of thigns could - for example the nexenta simply being overloaded. You only show one side.

I sugest:

  • Replace the nexenta with another box and measure network speeds. Even crossover cables can be defective. Check this one isn't.
  • Check network settings on both sides.
  • Tell us why we should not think the Nexenta is just totally overloaded.
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