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How Many CDs Can You Burn at Once?
kfs27 asks: "In an attempt to help a professor of mine record and duplicate his lectures. I have been asked to put together a CD duplicating box. Commercial products seem to be very expensive and I figured a PC with some SCSI160 Cards (HW or SW Raid maybe), SCSI Burners and a 15K RPM drive (size not an issue) could do the job for cheaper. But the question is, how many CDs can you burn at once of 30 minutes, mono audio. 10 at a time would be excellent I think. More of course better. Cost is not a huge issue, as long as it's less than Commercial Duplicators, it's more of an experiment, but must be stable and easy to operate (I'd be willing to script up a frontend)."
With the prices of RAM being as low as they are, you might want to consider building a ram disk to store the data that's going to get burned. That way you don't have to worry about the speed of the hard drives, the ram will always be faster.
We have one box here with 4 SCSI burners in it with a 700 meg ram drive. Everything works wonderfully in it.
You wouldn't want to mount the ISO as a filesystem (I assume you're talking about using a loopback device), because then you'd need to recreate it for each CD you want to burn - that would be pointless. You could mount the ISO in a 700MB ramdisk if you wanted, but that shouldn't be necessary. You just need a large software buffer. I use cdrecord with a 32MB fifo, creating ISO images on the fly, and that buffer never drops below 85%. That buffer would be ridiculously large if you're just burning an image directly off the hard drive - you could probably get away with an 8MB buffer for each drive (each drive still has an internal buffer on top of that), meaning you'd only need 80MB to burn 10 CDs at once.
I definatly wouldn't suggest the x86 archhetechture. in that case, with no cost problems, and at a university, you might be able to a) buy an old sun workstation from another department, or b) permenantly "borrow" one from the local research department...
as i recall, the sun and sgi workstations have really wide pci busses, which was what people on a recent macslash thread were debatinng why apple still has a long way to go to dethrone the two big S's in terms of personal rendering stations.
for a home solution, or at a eshop of sorts, an old sparc station or the likes might be out of the question, but if you're going to hack together somthing, just drop an old S motherboard, 10-20 cd burners, and a powersupply into a metal box, and let er' burn.
moox. for a new generation.
If a CD holds 660 MB and holds 1 hour of audio, that's a data rate of 11 MB/minute. Burning at 24x, that's 264 MB/minute. Bandwidth of a 64-bit wide PCI bus at 66 MHz is 528 MB/second, some 120 times the requirement of the single CD drive. It would appear that one could burn 10 or 20 CDs at a time at 24x and have plenty of bus bandwidth left over (so long as you were burning in parallel).
I'm not qualified to judge the architectural features which might create other bottlenecks, but neither the hard drive nor the machine bus appear to be a difficulty.
Scientists restrict study to entire physical universe; creationist
Burning multiple discs at once does sound nice at first, but there is one thing you seem to have overlooked : bus contention. No matter how many hyperfast SCSI cards you put in there, they will all share the same PCI bus and they will all compete over whose data stream is most important. This leads to reduced total throughput and greatly increased latency.
One thing you could try instead is to just use a bunch of older P2-300's with IDE burners and stream the audio files from a fast NFS or SMB server. Burning at 8x requires about 1400 KB/sec, so good ole 100base-T could serve 4-5 clients without a hiccup. Throw in 3-4 nics and you could have yourself a burner-cluster for very cheap.
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- Buy enough RAM to hold the entire image of whatever you're burning - but don't make a RAM disk to store it in. The OS will do just fine caching it (my twin 18 gig SCSI drives that I got on the cheap evidence this - my computer barely reaches for them after the first hour of uptime. REALLY fast!).
- SCSI burners wanted. This might even come out costing less because of the fact that an IDE card can only take 4 devices, while you'll be able to push several times that on SCSI. IDE will suffice for the HD if you're only burning one image at a time though.
- Avoid theoretical numbers. Worst case scenario all the way. Assume that even if you start all your burners at the same time, they'll have drifted by the end of the cycle. And as you do more and more reloads, I can see the timings differing. This won't affect reads of the image (it'll be cached), but writes will hurt. Get a SCSI card and wide enough PCI bus (shoot for 64/66) to take it. Sure, theoretical measurements say you'll hack it with a 32/33, but keep in mind that others things run on that bus besides just what you plug into the slots - and that's assuming 100% efficiency.
- SCSI stressed again. Bus mastering will help your CPU SSSSOOOO much. And yeah, I can't vouch it'd be that great on the ide -> scsi deal - but it's cached in RAM and RAM -> SCSI will help the proc.
- Hardware you'll want: 1 Gig of RAM (why skimp? A full CD is 700 meaning that you'll probably buy 768 (multiple of 256 - derr!), so shoot for the gig to play with. Any CPU P-III or better will do, maybe even a P-II. I'd just go pick myself up a decent Athlon though. As for the Mobo - Dual Athlon model. No, you won't use that second proc, but you will use the onboard Ultra160. If you can get one with dual channels - bonus! This is because you'll be capable of handling 30 drives.
Consideration: You'll have to have something to change out the discs. Set up with 10 drives, you should be able to EASILY do this for ~$2000. It's up to you to figure out way to change the discs automatically, though! And good luk on the caseSIG: HUP
First of all, if these MUST be in standard CD-audio format, then the answer to the question about how many disks you can burn of 30 minutes of audio in a given time can be calculated by dividing 30 minutes by the speed of the reader (say 15x), and then adding a minute or two for lead-in lead-out, toc, loading, etc. In this case, a 15x drive should be able to burn a 30 min CD in about 3-4 mins. A single drive should be able to turn out around 15-20 an hour.
The poster did say he wanted to do this on the cheap. The bandwidth bottleneck in a PC environment will most likely be the PCI bus. Even with two IDE drives on an IDE chain, you should be able to keep up with the burning at 15x (150MB/min per drive). If I was going to do this on the cheap, I'd get me a used Pentium-II/Celeron class machine, or possibly a higher end pentium machine, get 4 IDE chains in it, and load it up with 6 CDR drives. Total cost should be under $1000, assuming you use linux or freebsd or similar. ($600 for drives, $50 for controller card, $350 for used machine). You may need to add a little for memory expansion, as I think the idea of a Ramdisk (300Megish) would be good, but memory is cheap (512 total MB should be sufficient). If you need more drives, add another machine. If you find that the machine can't keep up with this many, drop one or two and put them on a second machine.
If these are for delivery to students which aren't at the lecture, or for review, perhaps the best thing would be to not focus on bulk duplication, but instead to figure out an on-demand system. What I mean is that if a student WANTS the lecture, then they can visit a computer at a specific location, select the date of the lecture, insert media and wait 5 mins for it to spit it out. That would be *Really* cheap (linux box w/CDR and suitably sized hard drive).
re-read the question. go ahead, I'll wait. done? good. He did say ~30 minutes of mono audio. now go sit in the corner with the pointy cap.
worked fine for us, the CD tower had 5 Plextor SCSI CDRW drives (Can't remember the model #'s offhand) external scsi connectors to an adaptec scsi card in a PC next to it, placed cd to be copied in the CDROM drive of the PC and up to five blanks in the tower, used Nero 5 software, Disk Juggler if I remember correctly would also work, I'll see if I can dig up more detailed specs if you need them. The PC was a Windows NT 4.0 Machine, with very little loaded onto it.
Keith