USB 2.0 vs FireWire?

[Chris Ruprecht]

David,

thank you for the explanation, specially the "FireWire is much faster" 
bit ;). Yes, indeed it is much faster then USB 1.x.

to clear up some variables:
The machine in question has 8 internal SCSI drives, the 4 GB file 
resides on one of the drives. It doesn't have a DVD drive that I could 
use for the test, and I suppose the DVD drive would be slower than the 
external drive anyway.

The external drive only uses one of the two possible connectors at any 
one time and I completely powered both, the server and the drive, down, 
before conducting the test.

The external drive was blank when I started this test (mke2fs ...).

The pm_10.d2 file is a single large (4 GB) database extent of a database 
that is completely shut down. You might say that it is equivalent to a 4 
GB DVD ISO image, except for the content, which, for this test, should 
not be relevant.

I have since tested this on another machine, an IBM eServer xSeries 342 
running CentOS 4.4, with similar results. I don't think this issue is 
only related to FC, I think it's related to Linux in general. I don't 
have Windoze installed on a server, but I will test this on my other 
desktop box which has built-in as well as another FireWire card. But 
that will only happen tomorrow.

Best regards,
Chris


David Timms wrote:
> 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.
>