Nogat

My company stores quite a bit of important data on DVDs. We currently are paying around $6 per DVD. Our purchasing manager found "Generic DVDs" for about one quarter of the price. Is this dangerous? Sounds scary to me...

RZA

Generally, you get what you pay for. In my opinion, I would stick with reputable media or whatever has been working well for me. In case of data, I wouldnt want to purchase cheep media and have it die on me ...and there goes my my backup

Not all media is created equal. Cheep media usually fails to burn properly and are rendered useless.

Even with a successful burn, the question of durability and longevity remains key. All burns produce a certain number of errors -- the CD and DVD data protocols are designed to handle this. But too many errors can result in a disc that does not stand the test of time -- readable in the short term, but possibly not years later.

Some media can burn reliably faster than its rated speed. A DVD+R might be rated at 4X burn speed, yet with certain recorders, it can be burned at 8X.

The factors that contribute to high- or low-quality media are varied. Several choices of dye are on the market, and which one is used can affect a disc's reflectivity, and thus its readability. But beyond that if your dye is unevenly spread, or the other materials and workmanship are shoddy, it doesn't matter what dye is used.

oshwyn5

http://en.wikipedia.org/wiki/Optical_disc

Okay, here is a broad general explanation which should answer your question, I hope.

When an optical disk (CD, DVD) is made commercially; an acrylic disk is covered with a layer of metallic foil and a mechanical press stamps this foil to make pits. which will reflect the read laser differently than the flat undisturbed surface. This foil layer is then covered with a protective surface (in some cases another acrylic layer in others merely a label). Damage to the lower acrylic layer can be polished out, but if the top layer is damaged and the foil marred, the disk is not repairable.DVDs store more data than CDROMs so the pits are smaller and the focus and pitch of the laser must be more precise.

Now we come to Recordable optical disks CDR and DVDR either + or - (the difference I will cover later)
The lower acrylic disk has a spiral groove cut in it and an optically sensitive (changes color when exposed to the right frequency and power of light) dye is put in this groove and then covered with either reflective foil or a doped layer of acrylic to accomplish "total internal reflection" as is done in fiber optics, where the refraction caused by the medium change will completely reflect certain frequencies of light (but be transparent to others) . The burn laser burns this dye , thus changing its color and hence the ability of the read laser light to pass through it . Once burned, this dye cannot change back ; so disks may be burned but not erased.


Rewriteable disks are similar , but use a liquid crystal (or liquid metal ) in place of the light sensitive dye; which at one power level will crystalize in one direction causing light to scatter, and when hit with a more powerful level will remelt and return to the original reflective state.

Now how does the drive know what type of disk it is? In the very center (all optical disks start at the center and work outwards) is a thin metal ring with the information needed for the drive to know what type of disk it is, what speeds it is designed to be burned at , and what power levels are needed to read, write, rewrite, erase etc as applicable. Then there is a "test" area for "calibration" of the needed lasers .

So now you know the difference between the different types of disks and how the drive determines which you have and what it needs to do to use them (note that this explains the calibration failed errors, if the calibration area of a write once disk is full or if the laser cannot meet the requirements of the disk you are using you get a calibration error). But what is the deal with the + and - .
Well these are "formats" or different manners in which the data is saved.
Just like when they first came out with video tapes there were two competing standards Beta by Sony and VHS by Phillips because of licensing restrictions of the original format so two different groups came up with differing standards for recording to DVDs. DVD-R was first, but some companies did not like the licensing and royalty scheme so they came up with their own format DVD+R . Think of it this way, one format the spiral is wide and the burn is perpendicular to the direction of the groove. The other the spiral is narrow and the burn is in the direction of motion. So in one you have a bunch of ------ along the spiral to represent data, and the other they are | | | | . Likewise, one may locate the position of an entry by dividing the whole disk into pie slices and then give a slice and ring number; while the other may just give a linear distance along the spiral relative to set points of reference.

Now obviously you cannot burn one format on a disk designed for the other and you cannot burn one with a drive designed to burn the other. So many modern drives can burn either format depending on which type of disk you have.
DVD-R disks tend to be cheaper, but DVD+R tend to support higher burning speed.
So what about burn speed? Well for a blank disk, the burn speed represents the fastest speed at which the manufacturer guarantees that you can burn data. This has to do with several factors, but think of it as some dyes and liquid metals require less energy to change state while others require more power or a longer burn time . So the shorter the time it takes to alter the dye, the higher the burn speed
Again, this is not a completely technically correct explanation, but it is putting things in "laymans terms" so you can get the idea.

DVD technology writes in smaller "pits" to the recordable media than CD technology. Smaller pits mean that the drive's laser must produce a smaller spot. DVD technology achieves this by reducing the laser's wavelength from the 780nm infrared light used in standard CD drives to 625nm to 650nm red light.

Smaller data pits allow more pits per data track. The minimum pit length of a single layer DVD-RAM is 0.4 micron as compared to 0.834 micron for a CD. Additionally, DVD tracks are closer together, allowing more tracks per disc. Track pitch-the distance from the center of one part of the spiral information or "track" to the adjacent part of the track-is smaller. On a 3.95GB DVD-R, track pitch is 0.8 microns; CD track pitch is 1.6 microns. On 4.7GB DVD-R media, an even smaller track pitch of 0.74 microns helps boost storage capacity.

These narrow tracks require special lasers for reading and writing — which can't read CD-ROMs, CD-Rs, CD-RWs, or audio CDs. DVD-ROM drive makers solved the problem by putting two lasers in their drives: One for DVDs, the other for CDs.

http://www.imation.com/products/dvd_...fferences.html



So what are some considerations quality wise between name brand and generic competitors? Well the generic does not pay for advertising, but does not get to charge $6 a disk ( I just bought a 25 disk spindle of GQ DVD disks for $3, that is 12 cents a disk over the weekend). While there in theory may be lower standards in the quality of the acrylic, the stability of the Dye used , the thickness and quality of the sealed edges ; I have seen no tests to indicate that this is so. (In theory low quality dies may be more subject to deterioration over time and if the edge is not sealed correctly and you live in the tropics and store your DVDs outside in the rain forest or under your bed they could potentially have a mold penetrate and eat the organic dye).
However, let me say that I have used generic CDROM disks for at least seven years now and none of mine have ever failed due to a cause such as this. (In fact my only problem with cdroms was a data backup on a name brand where somehow the table of contents got corrupted in the burn and when I put it back to restore the data windows told me that the disk contained 4 Terrabytes of data and I needed a bigger hard drive ; fortunately I do incremental and full backups on a regular basis so I just used the last full and incrementals ). I have been using GQ (Great Quality) DVDs which I guess qualifies as generic at least from a price standpoint for about three or four years now and none have failed . In fact I never got a coaster from a burn with them. Now others will say they are not any good. But I have one machine which barfs if you put in a Sony DVD blank and another that just throws coasters if you use Verbatim or Fuji.
My advice is to try a few of a brand and see if they burn successfully. If no coasters then you buy a larger batch or even a spindle and use them. If you get coasters; chances are that your machine just does not like their ink and is not calibrating correctly for the burn. Not the disks fault and not the drives.
Then you make sure that your disks are properly stored in a temperature and humidity controlled place out of direct heat and sunlight. You do regular full and incremental backups and periodically test the oldest and random sets to ensure there is no damage. If you find you seem to be experiencing problems with an older disk; you reburn all those from that date forward.


Personally? I would not be paying $6 a disk. At that price you could burn fifty copies for every one you are now. Expand on this and the probability of failure would have to be fifty times that of what you are using to justify the cost.

GQ DVD+R 4x 25 pack $4.99

DVD-R 8x 50 pack $12.99

I am sure you could find similar products ad lower prices

ebackhus

I bought 100 from Newegg.com that are purple back 4x burn DVD+R's for $38. So far they work GREAT and have stood up to a good deal of abuse. If I were to recommend brands I'd say Verbatamin. Avoid Memorex!

please

Verbatim 8X+R discs are on sale at newegg for $23/100 after rebate. These are some of the best disks available at any price.

It will take just one time of having your data corrupt and inaccessible to make the $$$ your company saved buying cheapo disks seem like a really bad choice