Firewire speeds

[Jeff Mueller]

I’m pretty much a newbie here, but I’ve been learning a lot, so I’ll try to share (just take it with a grain of salt):

According to Wikipedia:

IEEE 1394b-2002[21] introduced FireWire 800 (Apple’s name for the 9-circuit “S800 bilingual” version of the IEEE 1394b standard) This specification and corresponding products allow a transfer rate of 786.432 Mbit/s full-duplex via a new encoding scheme termed beta mode. It is backwards compatible to the slower rates and 6-circuit alpha connectors of FireWire 400. However, while the IEEE 1394a and IEEE 1394b standards are compatible, FireWire 800’s connector, referred to as a beta connector, is different from FireWire 400’s alpha connectors, making legacy cables incompatible. A bilingual cable allows the connection of older devices to the newer port. In 2003, Apple was the first to introduce commercial products with the new connector.

The full IEEE 1394b specification supports data rates up to 3200 Mbit/s (i.e. 400 megabytes/s) over beta-mode or optical connections up to 100 metres (110 yd) in length. Standard Category 5e unshielded twisted pair supports 100 metres (330 ft) at S100. The original 1394 and 1394a standards used data/strobe (D/S) encoding (renamed to alpha mode) on the circuits, while 1394b adds a data encoding scheme called 8B10B referred to as beta mode.

Now, as far as I can tell, 1 Megabit = 125,000 megabytes, but that doesn’t make any sense based on the Wikipedia stuff (or maybe it’s just late at night). Anyway, practically speaking I believe that FW400 does a bit less than 400 megabits, FW800 a bit less than 800 megabits and USB 2.0 about 480 megabits (but there are other reasons why you don’t want to use USB). I am currently editing in native HDV and using an external FW400 connection (400 megabits, yes-but it’s a fast 7200 rpm 32 mb cache drive) as my scratch disk and experiencing NO PROBLEMS as far as hard drive goes (render issues, but that’s different), so I think (but stand to be corrected) that it’s safe to say that a FW800 connection would be fine for anything short of a complex multicam or uncompressed HD set up (and yes you can buy FW800 raid arrays).

Hope that helps, and ready to learn from the gurus.

Best,

Jeff

Jeff Mueller
http://www.ApertureVideos.com
Santa Barbara, CA

[Rafael Amador]

1 Byte= 8 Bites
The 800 Mbps means a theoretical transfer of 100 MB per second.
Rafael

http://www.nagavideo.com

[Steven Gladstone]

Yes, thanks for the help, but I’m trying to find out in a practical application, if I have two Firewire 800 drives daisy changed together, how many MB/sec ought I expect to get transferring data? In an Hour how many Gig can I transfer?

I just purchased a second drive, and I’m concerned it won’t be fast enough, especially daisy chaining the two. If so, I’ve got to send it back.

All the theoretical stuff is nice, but real world is the importatn thing. Perhaps there is a utility for testing this?

Thanks.

Steven Gladstone
https://www.gladstonefilms.com

[Jeff Mueller]

It was very late when I wrote the first post, but I had meant to describe what I am doing in case it is relevant to you, but again, I am a technical novice and I certainly haven’t measured actual speeds. Everything I’ve read says that the back end of a daisy chain will be slower. Of course there are Raid arrays like G-Raid and ethernet options like the D-Link box, this is just my no budget approach, but for my purposes it is working.

I have two LaCie external drives, both 7200 rpm and 16 mb cache. One is plugged into the computer via FW 400 and serves as my scratch disk and render storage. The second one back is connected to the front drive (via FW800 but it’s limited to FW400 speeds by the first connection)and serves as my backup disk. I’ve also cloned my OS and programs onto a partition and as an experiment I have booted the computer over the FW400 connection and it works without problem.

I have been editing HDV and working extensively in Color and have had no problems or speed issues as far as the drives are concerned. The only problem I had (and completely understandable) was when I tried to boot off of the same FW drive I was using for Scratch (just a test mind you) I got a message that basically said your drive’s to slow. Now if your editing multi-cam or uncompressed HD that’s a different story, but if your working in a similar manner to me, and have everything strung together as FW800, I can’t imagine you’d have a problem as the penalty for daisychaining is probably not as big as the drop down to FW400.

I do have other problems with my system, but not the drives. Hope this helps.

Jeff Mueller
http://www.ApertureVideos.com
Santa Barbara, CA

[Rafael Amador]

Hi Steven,
Yes, the transfer rate won’t depends only of the FW interface.
Will depends also of the HDs you are using and the FW busses you are using (1 in your case).
If you want to test the transfer speed of your HDs you can download the “AJA System Test”.
In the Activity Monitor> Disk Activity you can see the Read/Write speed of your HDs.
Keeping clean the HDs directories will make them work faster.
rafael

http://www.nagavideo.com

[Steven Gladstone]

Great, thanks. Will do that – now to find the AJA system test, but that is what the internet is for.

Steven Gladstone
https://www.gladstonefilms.com

[Rafael Amador]

Hi Steven,
Is included in the AJA Utilities and comes with KONA or ioHD drivers.
In https://www.aja.com.
Cheers,
rafael

http://www.nagavideo.com