View Full Version : Raid for Video

03-08-2002, 05:45 PM
I am looking at putting together a Raid0 system for video capture/editing. Right now I am leaning towards the ATTO Ultra3 Single board with two Seagate Cheetah 18.35GB Ultra160 4MB cache. I just wanted to know if I would see significant performance increases by using Ultra320 drives, and under what circumstances would I want to use the double instead of single channel boards. The computer will either be a g4 733 or g4 800 DP so any opinions about that choice would be welcome too. The setup will be used to capture and edit video and dv in an educational environment, and my total budget is about $7000. This is my first Raid so please, be gentle.


03-08-2002, 08:27 PM
I have nearly that same setup My biggest question is how much video are you planning on capturing at one time? 2 drives will give you about 34 usable gigs and it fills up QUICK! DV Runs about 13gigs an hour and analog runs higher than that!. If you will be capturing mainly short bits of video then the 2 drives should do it AND you will save significant $ by not having to get an external enclosure & cables.

If you are planning on 2 drives you will only need a single channel card. It has been proven that having 2 drives on seperate channels gives only a very small speed increase and to most ppl is not worth the added expense. When you move up to 4 drives then 2 channels give you more benefit.

2 drives will fit inside your Mac but I recommend that you get the U320 15000 rpm drives. Not only are they faster but they run cooler! They also have twice the cache onboard.

My raid is 4 drives (U320 15000rpm Cheetah) in a 2 channel external Burly enclosure. I have 2 ATTO scsi cards in my Mac (G4 733) one dual and one single channel. I must say that they are rock solid boards I have never had an issue of any kind. I mostly run OS X but have occasionally booted 9.2 as well.

03-08-2002, 08:46 PM
Welcome rh,

For someone who says it's his 'first raid be gentle' you ask great questions and sound like you really have a pretty good handle on the issues.

Damien seems to have covered the high points, don't forget to plan your cables and termination. Granite is definately the way to go, when you figure out your configuration we'll be happy to double check what parts and pieces you'll need to order.

For pure speed 2 channel is faster than single when you have 4 drives or more, but you shouldn't need 2 channel ever, 4 drives will do real well on a single channnel as well. I hadn't tested that configuration but I will tonight, I haven't started using the 4 drive UL3D raid yet and can simply reattach the cables for single channel use and test 'er out. I'll post back if it made a huge difference.

Hope we can help make this fun and easy.


03-11-2002, 12:00 PM
Forgive my ignorance again, but if I have two 18gb drives on Raid0 the computer just sees one 18gb volume correct? Thanks for the info BTW very helpful!

03-11-2002, 01:19 PM

RAID0 is striping. When you stripe two 18gig drives together you will see one 36gig volume. Striping is a way of 'adding' together the throughput of more than one hard drive to gain performance. Data is written to more than one drive concurrently which is how you get a speed increase. A failure of one drive will make all your data unreadable on all drives on the RAID.

RAID1 is mirroring. When you mirror two 18gig drives you end up with a copy of one drive on the other. Two 18gig RAID1 drives effectively net you 18gig of space. No speed increase comes from RAID1, this is for data protection.

In talking over the UL3D vs UL3S it was pointed out to me by Kaye that I should point out the Single channel card only allows 160 MB/sec max transfer rates where the Dual channel card allows 160MB/sec transfer rates per channel. If you install 3 or 4 drives on the single channel card you will soon max out the 160MB/sec pipeline and no gains will be had in speed. However, there was method to my madness when I said that the single channel card would be fine, you shouldn't need more than 160MB/sec for DV anyway.

There is probably little reason to build a 2 channel raid for DV, the reason to get a 2 channel card is future expandability and segregation of devices if you ever purchase scsi drives that have significant speed differences. LVD buses always perform at the level of the slowest installed device. Having a second channel reduces the possibility that during a capture your bus slows down and florfs your data.

It seems that drive capacity and reliability would be more important than top speed. You can add together performance via RAID0 striped drives and easily achieve the needed performance for DV. Having the larger 8MB buffer can really increase measurable performance also.

I do not have any DV experience at all. I use my RAIDs for Photoshop and general computer acceleration. Please, double check that the issues of continuous and unbroken data transfers required by DV are addressed by someone in the know.

Hope that helps some. Fun project.


03-11-2002, 05:55 PM
i am doing a lot of DV right now but I do not claim to be "in the know" However, I have a 4 drive raid on two channels and have never had a dropped frame that I know of. Also I started with a single channel 2 drive array and had no issues there either. I read that DV had a ridiculously low requirement for sustained write of your HD's at least compared to analog capturing.

With a raid you will never have that annoying message from iMovie...

" The response time of your pitiful, puling little ATA drive really blows, get a real drive" (Ok maybe that's not word for word......)

03-11-2002, 06:14 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>by damienI read that DV had a ridiculously low requirement for sustained write of your HD's at least compared to analog capturing.<HR></BLOCKQUOTE>

I'm by no means in the know either, but it kinda makes since that DV only needs "wimpy" performance. Most every new Mac or PC comes with ATA drives installed, so the spec would have to utilize some sort of "normal-standard".

BTW, what is the translation of "analog"? I know that it must be huge, because all the post houses (mostly) use FibreChannel RAID's.

03-11-2002, 06:47 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>It seems that drive capacity and reliability would be more important than top speed. You can add together performance via RAID0 striped drives and easily achieve the needed performance for DV. Having the larger 8MB buffer can really increase measurable performance also.<HR></BLOCKQUOTE>

I think the main issue with DV throughput is AFTER you have captured the video. If you have 1 hour of MPEG2 video (highly compressed) then its about 4GB of data. The capture rate of 4MB/s * 60 = 240MB/minute * 60 = 14.4GB/hr http://www.macgurus.com/ubb/eek.gif ! Now if you work with uncompressed analog video - that goes WAY up.

The standard DV is 4:2:2 standard (4 is 8bits and 2 is 4 bits - IIRC - its strange, but that is the convention). I have not worked much with DV, yet but I find I often have a LOT more footage than I really need. I guess I somehow picked this up in college where I would often have to whittle down my reports so the prof would actually have time to grade it before the semister was over.

Here are some articles from http:/www.xlr8yourmac.com
200GB+IDE RAID (http://www.xlr8yourmac.com/IDE/quicksilver_raid/quicksilver_IDE_RAID.html)
More IDE/ATA RAID (http://www.xlr8yourmac.com/IDE/IDE_RAID_Card_reports.html)
IDE RAID - HOW TO (http://www.xlr8yourmac.com/IDE/IDE_RAID/driveinstall.html)
They are a bit dated, but should give you a good idea. Its also good to stay away form the bleeding edge and I often like the trailing edge myself - more tested, less expensive and better roadmaps. SCSI is definately something to consider since you get a much longer life - 5yrs vs. 3yrs under warranty. Also Seagate really backs their products up and they do make some good IDE/ATA Barracuda drives.

The Cost Of Freedom:
Every bit of energy.
Every ounce of courage.
Every drop of blood.

03-11-2002, 11:39 PM
I tried analog for a while on a completely empty 7200 rpm IBM ATA66 drive (single master) that would bench at 35-38MB per second and I had too many dropped frames to make it worth my while. 640/480 high qual. (which is not even at the pro level) Using an Aurora Fuse card it ate up about 20+gigs an hour