Network Speed Vs Hard Drive

[maruko]

This is a nerd question, so my friend and I had a discussion about max sustained speed for a hard drive. I said that your normal 7200rpm drive can sustain a bandwidth that would not be close to the 100 mega bits or what ever a standard 10/100 switch can push. He was telling me how the 100 mega bits divide by 8 would be say 12 megabytes. And for sure a hard drive can sustain more than 12 megabytes. So in my 100 switch, the limiting factor is the switch and not the hard drive. So to make max use of bandwidth, switches should be gigabit. But I've always though the limiting factor in current networks was the PCs themselves and not the network. I've always though gigabit was for servers/high end pcs/or connecting switches.

I'm so confused right now! Can someone shed some light for me?

[bbrian]

You're friend pretty much has it right.. 100mb/s Ethernet = 12.5MB/s

The other factor that you didn't consider is that there is significant overhead within Ethernet and TCP/IP. I don't remember the exact figure, but the payload on a packet is approximately 30%, meaning there's about 70% overhead (tcp/ip overhead + Ethernet overhead), plus you have 'chatter' (arp, etc) on the network that isn't transferring any of your data that is also taking up bandwidth. It's been a while since I've looked at anything at this level, so please excuse the cheesy explanation.

However, rarely are you streaming that much data across the network at once. Networks are 'bursty', which is what makes it work so well. While you're network would probably be significantly faster with a gigabit switch, I doubt your network is actually busy enough to justify it. If you are buying a new network anyways, go gigabit. If you already have a good network up and running, I'd leave it until something breaks and needs replaced.

[Kevster]

If you wanted to improve your overall network performance, you can add an additional 10/100 NIC. Or you can go the gigabit ethernet route as well.

In most server architectures, the disk subsystem is the limiting factor more than anything. While the transfer speeds may say 100MB/s or 133MB/s for ATA 100 or 133, that is a burst speed only. What your actual sustained throughput mey be will depend on the access time for the drive, drive speed (rpm), the amount of drive memory cache, etc. There have been many papers written on this subject so a refined google search may point you to your ultimate answer.