Why does copying over a network take so long?

June 1, 2007 at 1:31 pm Leave a comment

First, some background:
I use Sage TV, a great application that can turn your Windows machine into a real TIVO killing PVR. To top it off, it is networked, so you can write everything to a single server (with multiple TV tuners in that box) and you can connect in from a remote client machine (or even a network attached set top box they sell) and watch it around the house. Awesome functionality.

The down side? Well, with any PVR solution, you are going to start having to deal with absolutely Ginormous (Gigantic + Enormous) files. In my situation, I have like a hundred shows that have been saved off for the kids, and probably another hundred shows that my wife either hasn’t watched yet, or wants to keep. Most of these files are in the 2 GB size range. Normally, this isn’t a problem since you probably aren’t copying them all over the place. If you do need to copy them off for any sort of system maintenance, though, this can be a problem.

I recently went through this myself, copying literally hundreds of files across the network to my new ReadyNAS NV+, then later copying them back, and it took SOOO long to copy. I’m talking hours and hours.

To illustrate why, I did a bit of math:

The theoretical maximum speed of 100 Megabit Ethernet (with absolutely no protocol overhead) can be calculated this way:

100 Megabit = 100 million bits per second = 100,000,000 bits per second
There are 8 bits in a byte, so 100,000,000 / 8 = 12,500,000 bytes per second
Convert bytes to Megabytes:
12,500,000 / 1024 / 1024 = 11.92 MB/second
11.92 MB/second = 715.2 MB/minute = 41.9 GB/hour

So, without the overhead of any protocol at all, the maximum speed you could hope for with 100 Megabit Ethernet is about 41.9 GB/hour.

That’s why copying over a network is so slow – Because I have GINORMOUS files…

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Entry filed under: Networking.

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