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I have a Belkin N600 dual band router. On the network typically are my PC, 2 iPhones & 2 PS3's. At times there can be another PC and a couple of laptops.

I have configured the router so that the 2.4GHz band is B, G or N and the 5GHz band is N only. I also have a WD ShareSpace 4TB NAS wired directly into the router LAN port.

My PC has a Belkin N USB adaptor.

What I find when transferring files from my PC to the NAS box is that transfer speeds don't get above 2MB/s and typically are between 750KB/s and 950KB/s. On the task manager, link speed varies between 76MB/s and 20MB/s. Signal strength is usually very good or excellent. I understand that I am never going to get 300MB/s out of this and to be honest I'd be happy with 20MB/s but 2MB/s is somewhat disappointing.

I have even gone to the lengths of removing all other items conected to the network except my PC. Even after a full reset of router and restart of PC just in case, the speed is still only 1MB/s.

Any ideas?

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So how can I resolve this and when I have how do I allocate bandwidth to specific devices so that my PC gets a bigger slice. –  Rob Apr 16 '11 at 20:57

1 Answer 1

I think you're confusing MebiBytes/s (1,048,576's of 8-bit bytes) with megabits/s (1,000,000's of single bits). Local disk and file I/O is usually measured in MebiBytes/s, whereas network link speeds are usually measured in megabits/s.

Talking about remote fileserver performance requires caution because it's file I/O that rides on top of network I/O, so filesystem engineers (and file copy performance tools) want to talk about it in MebiBytes/s and network engineers (and network performance tools) want to talk about it in megabits/s.

Your Belkin N600 is capable of up to 300 megabits/s signaling, but you beware that Wi-Fi has a lot of overhead, so the rule of thumb is that your TCP throughput on Wi-Fi is usually about half your signaling rate. So 150 megabits/s, which is roughly 18 MebiBytes/s. But that's in idea RF conditions, with ideal TCP usage. Once you add the overhead of a remote filesystem protocol like SMB and whatever app you're using to do the copies, I think I'd be happy with 15 MebiBytes/s.

Then there's the question of how much throughput your WD ShareSpace 4TB NAS is capable of. According this review at SmallNetBuilder, that box is pretty slow and can only get about 20 MebiByte/s sustained throughput even on gigabit Ethernet. If that slowness is due to latency issues, then it'll have a big impact on what kind of throughput you can get from it even over wireless.

When you say "On the task manager, link speed varies between 76MB/s and 20MB/s", is that in reference to the network interface link speed or the file copy speed? And are you sure it's in MebiBytes/s or could it be in megabits/s? I would expect megabits/s since it's a network link.

If your Wi-Fi signaling rate is only 20 megabits/s at times, then your ideal TCP app throughput would be about 2.4 MebiBytes/s, further degraded by the WD ShareSpace NAS's latency and SMB and app copy overhead, and your 750 KibiByte/s throughput starts to make sense.

If I were you, there'd be two main things I'd be doing to speed this up:

  1. Improve my Wi-Fi signaling rate to the 300 megabits/s the Belkin gear should be capable of. This might mean moving the PC closer to the AP, making sure wide (40MHz wide, HT40) channels are in use, making sure I selected nice clean channels in both 2.4GHz and 5GHz, and making sure my PC is joining on the less-likely-to-be-congested 5GHz band.

  2. Improve my fileserver latency by getting a faster device to act as a fileserver.

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Great reply, thanks. –  Rob Apr 17 '11 at 14:14
    
You are correct about Megabits and bytes, I did means bits but was a little careless with the capitols. I am begining to realize that the choice of NAS box was a little hasty but I'm stuck with it for now. I think the simlest was to get the transfer rates to an acceptable level may be to go for a LAN cable between the router and my PC. Mine is the only one that will be doing the heavy transfers the other gear will be mainly accessing those files and a couple of seconds delay while an image loads is not the end of the world. –  Rob Apr 17 '11 at 14:20
    
+1 for another crazy-good Wifi answer. –  Ƭᴇcʜιᴇ007 Dec 2 '11 at 0:56

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