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// Tales from software development

Read/Write speeds

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I don’t usually pay too much attention to the read/write speeds given in disk and flash drive reviews because I doubt that I’d really notice the difference of a few KB/s when speeds are measured in MB/s. But I’ve just done a quick survey of the read/write speeds of various devices attached to my development laptop and was surprised by some of the results.

I used Totusoft’s free LAN Speed Test utility. This simply writes some data to a file and then reads it. Reading and writing to a file share gives an indication of real world network performance. I used the default data size of 100Mb.

What got me started on this is that my broadband modem and a couple of servers are in a different location to most of my development PCs and the link between the two groups of devices is an ‘ethernet over power’ (EOP) type link. This is rated at 200 Mpbs although I was aware that, realistically, I was probably only getting around 40-50 Mbps. I’ve been meaning to run a CAT5/6 cable between the two groups and thought it would be useful to measure the performance of the link to see how much benefit I’d get.

When I ran the LAN Speed Test utility it gave me a result of 4 Mbps write (outgoing) and 2.5 Mbps read (incoming). I was shocked by this as it’s an order of magnitude less than I’d expected. I bypassed the EOP link using the built-in 54G wireless NIC in my devolopment laptop and got 19.2 Mbps write and 19.6 Mbps read. Things must be bad if a 54G wireless connection is 5 times faster than the EOP link!

Then I ran some more speed tests with the following results:

Device        Write (Mbps)  Read (Mbps)  Description
LAN EOP                4.0          2.5  LAN PC-PC ethernet-over-power link
LAN 54G               19.2         19.6  LAN PC-PC 54G wireless link
LAN Gigabit          287.6        276.7  LAN PC-PC gigabit ethernet link via 1 switch
LAN Gigabit (2)      121.9        355.6  LAN PC-PC gigabit ethernet link via 2 switches
Internal SATA        273.8        213.3  Internal 2.5 inch SATA drive
USB SATA             130.0        174.6  USB attached external 3.25 inch SATA drive
USB Flash             32.0         87.8  USB Flash drive
SDHC                  64.0        133.0  SanDisk Ultra III SDHC in internal card reader

The main surprise is that reading and writing over a gigabit LAN is faster than accessing an internal hard disk. I was sceptical enough to rerun this test a few times but the results were consistent. The test was reading/writing from my development laptop to a server, both with gigabit NICs and connected via a NetGear ProSafe unmanaged gigabit switch.

The performance of the EOP link was so poor that I decided it was time to replace it with a network cable. To make the most of the Gigabit NICs installed in some of the PCs I also purchased another NetGear ProSafe gigabit unmanaged switch to replace the built-in 100mbps switch of the broadband router/modem. I repeated the EOP test using the same two PCs. The link was now PC-switch1-switch2-PC (both switches are NetGear ProSafe switches). The result is shown as ‘LAN Gigabit (2)’. Replacing the EOP with a cable gave a 30 times improvement in write speed and a 142 times improvement in read speed. Again, I was sceptical of the reported read speed but I repeated the test several times and got the same result. Even increasing the data size to 1Gb to rule out caching didn’t significantly change the result.

The difference in performance between a USB flash drive and an SDHC card inserted into my development laptop’s integrated card reader also provided a small surprise. I thought they’d be about the same or that the SDHC card might be a little bit slower. This particular card is a SanDisk Ultra III high speed card optmised for use in digital cameras which might explain why it was so much faster than then USB flash drive.


Written by Sea Monkey

March 19, 2010 at 8:00 pm

Posted in Hardware

Tagged with ,

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