Speed Question

[nezzy999]

Hi Guys,

I have had a question brewing for a while and its really starting to bother me.

Basically how fast do (standard)hard disks write, I know there are a lot and results will vary but im only talking on a general scale.

7200RPM Serial Attached 250GB Hardrive (Seems like a general drive)

At what point does the hard disk write speed become the limiting factor.

Lets say I am downloading a large video file on a home network 100Mbps, 10MBps(allowing for overheads etc...) I know hard disks can write faster than this, but what if it was a 1Gbps ~125MBps, would this cause the hard disk write speed to become the limiting factor? Or would the internal connection to the hard disk bottle neck first?


Cheers Guys and Girls
Nez

[xcorvis]

Here's some average write performance data for a bunch of SATA hard drives.
http://www.tomshardware.com/charts/3-5-hard-drive-charts/Average-WriteTransfer-Performance,659.html

Here's the Max write performance:
http://www.tomshardware.com/charts/3-5-hard-drive-charts/Maximum-Write-Transfer-Performance,667.html

Note that's MB (Megabytes) not Mb (Megabits).

So yah, it looks like if you could pull a full Gbps you'd probably get the data faster than the drive could write it. Plus you'd have the overhead of the OS and all kinds of other stuff going on in your system.

The internal bus should operate much, much faster than the hard drive (otherwise swap space would be considered "fast"), so I don't think that would bottleneck you.

[nezzy999]

Thanks,

Just one more thing to put my mind to rest.

The external drive I currently have normally hits around 20-40MBps, this is backed up by the benchmarks a on extreme tech and tom's hardware.

So therefore there would be no benefit for me using an eSATA connection as the USB2.0 hits around 60MBps.

-------------

Finally if eSATA advertises 1.5Gbps where does a speed of 150MBps come from (I have seen it on a few sites) ?

[tokenuser]

So therefore there would be no benefit for me using an eSATA connection as the USB2.0 hits around 60MBps.No matter how fast your hard drive, you are still constrained by the fact that USB2.0 only has a 480Mbps throughput (and that is peak, not sustained).

Finally if eSATA advertises 1.5Gbps where does a speed of 150MBps come from (I have seen it on a few sites) ?1.5Gbps = 1.5 Giga BITS per second.
150MBps = 150 Mega BYTES per second.

The difference is that marketing never quite understood why engineering keep insisting there are 8 bits in a byte, and said "Ah screw it, lets say its 10 bits per byte and be done with it". They do it with hard drive space, and throughput ... but for all intents and purposes 1.5Gbps = 150MBps.

Now back to the first point USB2.0 is 480Mbps which does in fact equal 60MBps.

So, no matter how fast you try to pump data onto a fast drive in an external enclosure, you are going to hit the 60MBps bottleneck - and in realisty it will be less than that, because that is the theoretical maximum speed, but data throughput is rarely going to hit that.

Firewire (OK technically IEEE 1394) comes in two basic flavours Firewire 400 and Firewire 800. While slower Firewire 400 has a higher sustained throughput speed (400Mbps) so actually writes faster than USB2.0, and Firewire 800 is twice as fast again. A lot of laptops come with Firewaire ports (Macs definately, either 400 or 800 speeds) - so that might be an option to consider as well.

[white]

The difference is that marketing never quite understood why engineering keep insisting there are 8 bits in a byte, and said "Ah screw it, lets say its 10 bits per byte and be done with it". They do it with hard drive space, and throughput ... but for all intents and purposes 1.5Gbps = 150MBps.
Wow, that is screwed up! And I thought them saying there's 1000bytes in 1 KB was bad!

[nezzy999]

Thanks Token.

My head can rest now :D

[tokenuser]

Wow, that is screwed up! And I thought them saying there's 1000bytes in 1 KB was bad!It all started when the marketing departments couldn't figure out how to represent 8 bits in a byte, then 1024Bytes in 1kB, then 1024kB in 1MB, etc.

If only they had realised that if they had left their thumbs stuck up their collective asses, counting in 8 isn't so hard ... but nooooo ... they had to rely on base10 numbering.

[therage800]

So yah, it looks like if you could pull a full Gbps you'd probably get the data faster than the drive could write it. Plus you'd have the overhead of the OS and all kinds of other stuff going on in your system.



But then you just wait for USB 3.0 with its wapping 4.8 Gbps.