[Discuss] Possible backup scenarios for a 500GB drive

[John Blomfield]

Alan W. Irwin wrote:
>
> I cannot conceive how I am going to fill a 500GB drive, but that is 
> what I
> said about my 1GB, 2GB, 7GB, 25GB drives in their era, and also my 
> current
> 80GB drive.  However, I think it is a good prediction that the files 
> on the
> 500GB disk will only accumulate or change slowly so that any given run of
> rsync or dump will not have much to do.  USB 2.0 has a theoretical 
> transfer
> rate of 480Mbs according to http://www.everythingusb.com/usb2/faq.htm 
> so it
> is 4.8 times faster that 100Mbit networking, and 6.25 times slower 
> than the
> 3Gbps SATA II.  Of course, the factor of 6.25 is an overestimate of the
> speed ratio for the same drive interfaced with either USB 2.0 or SATA II
> since most drives have sustained data rates that are considerably less 
> than
> 3Gbps.
>
> Alan
You're correct USB 2.0 has a maximum theoretical rate of 480Mbps but 
since USB is a packet based protocol the actual rate is much much 
slower. I have seen some performance reports on some USB drives at 
around 30 to 50Mbps (this would be less if there were other devices on 
the same hub) and is therefore similar to a 100Mbps network which also 
has overhead.  But as you point out you should be comparing with the 
SATA internal drive and you will find the "effective transfer rates" for 
SATA compared to effect UBS rates will be much greater than 6.25.

I have used a simple removable HD tray for sometime. Its not as easy to 
plug in as the more modern versions but you just shut down, pull out the 
tray from a normal tower slot (at the front you don't have to open the 
case!) unplug the drive connector (data and power). There is a key to 
prevent unauthorized removal. When you power up again without the drive 
the BIOS thinks the drive has failed so you just reset the BIOS options 
and go.  When you replace the drive the BIOS will recognize it as a new 
plug and play drive so its not a problem.  I have found it very useful 
for checking drives removed from dead computers etc. without having open 
up a working computer case and installing the suspect drive in an empty 
drive bay.

John Blomfield
>