USB 2.0 vs FireWire?

[David Timms]

Chris Ruprecht wrote:
> Hello,
> 
> I have a Dell PowerEdge 2500 server with FC6 + latest updates installed.
> 
> For backup, I want to use 2 external disk drives, 300 GB each (all 
> internal stuff is SCSI). I bought a USB 2.0/FireWire combo card and am 
> running a few tests and to my great surprise, USB 2 (480 mbps) is way 
> faster than FireWire 400 (400 mbps). I get this from hdparm:
> 
> Connected as USB 2.0 drive:
> hdparm -t -T /dev/sdd
> 
> /dev/sdd:
> Timing cached reads:   948 MB in  2.00 seconds = 473.56 MB/sec
> Timing buffered disk reads:   76 MB in  3.03 seconds =  25.11 MB/sec
> 
> Connected as FireWire 400 drive:
> hdparm -t -T /dev/sdd
> 
> /dev/sdd:
> Timing cached reads:   948 MB in  2.00 seconds = 473.05 MB/sec
> Timing buffered disk reads:   32 MB in  3.07 seconds =  10.44 MB/sec
Notice this is only looking at read speeds.

> To make sure that hdparm is not messing with me, as the only reference I 
> find in its man page is relating to IDE and SCSI drives, I tested some 
> simple copy command of a 4 GB file. I did each command twice in a row, 
> to avoind any skewing of the results by anything in OS buffers.
> 
> USB 2.0 Mode:
> time cp -v /home/db/pm/pm_10.d2 /media/extd/xxx3
> `/home/db/pm/pm_10.d2' -> `/media/extd/xxx3'
> 
> real    3m20.819s
> user    0m0.988s
> sys     0m54.483s
> [root at mars ~]# time cp -v /home/db/pm/pm_10.d2 /media/extd/xxx4
> `/home/db/pm/pm_10.d2' -> `/media/extd/xxx4'
> 
> real    3m18.799s
> user    0m1.048s
> sys     0m54.791s
> 
> FireWire Mode:
> time cp -v /home/db/pm/pm_10.d2 /media/extd/xxx1
> `/home/db/pm/pm_10.d2' -> `/media/extd/xxx1'
> 
> real    7m33.109s
> user    0m1.196s
> sys     0m52.439s
> [root at mars ~]# time cp -v /home/db/pm/pm_10.d2 /media/extd/xxx2
> `/home/db/pm/pm_10.d2' -> `/media/extd/xxx2'
> 
> real    9m13.851s
> user    0m1.108s
> sys     0m55.191s
You are causing the data to be duplicated on the disk; this might slow 
down with each subsequent write due to disks generally being fastest 
transfer at the begining, and speed trailing of by 20% toward the end of 
the disk.

> I used the same drive, a Maxtor 320 GB drive that was on sale recently, 
> which is mounted inside an Adaptec external USB/FireWire combo case.
> 
> Any ideas why FireWire is so much slower than USB? Should I look at the 
> card, the drive or the drivers? I would really like to use the FireWire 
> side of things, but not at this ridiculous  speed.
With {probably} a different drive and dual interface caddy, my brother 
had seen similar results ie usb2 is about 2x the speed of firewire. He 
did notice that it is important to plug the second usb power header 
connector in or either interface could be much slower than expected. I 
think this might be because one interface /the drive might have been 
running close to minimum power limits. {his test was with winxp sp2 on a 
dell notebook}

The second thing to notice is that USB2 is a much newer standard. The 
original "firewire is faster" comes from a comparison with USB1.

Could you try another comparison by writing a single large file eg a 
dvd.iso to the drive ? I'd like to see the difference. Does it change 
much if you blank the drive, and then test via the firewire interface first.

Do you leave both interface cables plugged into the server when you are 
doing the test ? This might cause an extra slowdown.

Also, for reference, what is the size of your previous test {du -s 
whatever} ? And what did the write data-rate work out to be ?

It might be that a pure firewire interface would be better than the dual 
interface box.

In any case, for backups you probably want to use something like:
$ rsync -a /home/db/pm/pm_10.d2 /media/extd/xxx1

DaveT.