Mac Musings

DVD-RAM Gets Affordable

Daniel Knight - 30 December 1999 -

I was stunned to see blank 5.2 GB DVD-RAM media at $14.99 per disk on dealmac.

When we started archiving backups and large projects to DVD-RAM, it was tough to justify the media expense. We had to base the decision on random access and increased archival stability vs. backup tape.

That was a year ago, when AIT tapes sold for $100 each with a real world capacity of around 35 GB (depending on compression) while DVD-RAM disks were $42 apiece. By carefully removing about half the data from our backup tapes when archiving to DVD-RAM, we had roughly comparable media costs.

Not too long ago we rejoiced when DVD-RAM media dropped to about $35 per 5.2 GB double-sided disk - and now it's hit $15!

Of course, AIT has also dropped in price. If you shop around, you can get tapes for under $90 each.

Based on our last backup set, we're averaging 37 GB of data per tape, which comes to $2.43 per GB. DVD-RAM stores about 2.35 GB per side, for a cost of $3.19 per GB (alas, there is no compression when archiving between backup sets). Since we archive only about 50% of data on a backup set, we use $105 worth of DVD-RAM media to replace $180 worth of tapes.

If we were using DVD-RAM for backup, we would achieve about 30-35% compression, for a capacity of about 3.3 GB per side and a cost of $2.27 per GB with double-sided media. That's even better than the price of tape!

But we don't use DVD-RAM for backup at work for one simple reason: capacity. We're backing up a network of 80-some Macs. We can fill an entire AIT tape before every machine is backed up once. Were we using DVD-RAM, we'd have to have someone work through the first night of every backup flipping disks ever 3.3 GB or so. That just wouldn't be practical.

Worse yet, Apple seems to have picked the slowest DVD-RAM mechanism or drivers in the world of computing. Archiving data from tape to DVD-RAM takes about 3-3/4 hours per side. At an uncompressed capacity of 2.3-2.4 GB per side, that's only 625 MB per hour.

Most DVD-RAM drives and drivers are twice that fast, which means they can backup 1.25 GB per hour uncompressed - or about 1.75 GB per hour using software compression.

How does that compare with AIT? Well, that depends on what you're comparing.

Backing up our backup server to AIT with an Ultra SCSI interface, we have achieved speeds up to 218 MB/min. or 12.7 GB/hour, although our average backup speed is less than one-quarter that fast.

Backing up our G4s over 100Base-T ethernet, we get even faster backup, reaching as high as 235 MB/min. or 13.7 GB/hour. But scaling back to 10Base-T, we have a maximum throughput of about 85 MB/min. (5.0 GB/hour).

Compared with any of these, DVD-RAM is excruciatingly slow. On the other hand, it doesn't require a $2,000 tape drive, $400 Ultra SCSI card, and $90 backup tape. Apple's DVD-RAM is a $300 option on the Power Mac G4, the disks are now as low as $15 each, and there's no need to buy an interface. Still, you're looking at under 1 GB per hour backup speeds using data compression and the Apple drive and drivers.

Using a third-party drive and drivers, you can double performance. That means about 1.75 GB/hour, which still means several hours to back up 6 GB of data - and the necessity to flip the disk every two hours or so.

On the other hand, thanks to data compression, you can store up to 6.5 GB of data on a single $15 DVD-RAM disk, making it a very economical way to backup or archive large quantities of data.

But then there's the expense of buying a DVD-RAM drive (unless you're in the market for a G4). External SCSI DVD-RAM drives are now available at under $400, and internal models are even less expensive. Even at today's prices, DVD-RAM one-third the cost of an AIT drive - and it doesn't require an Ultra SCSI card.

Pixela has already announced a USB DVD-RAM drive, and I suspect we'll see one or more FireWire drives announced at Macworld or CES next week.

If you're looking for an relatively economical backup system with good capacity, DVD-RAM definitely merits consideration.