Optical Drive Cache...

[Quiksilver]

Does anyone know why optical drives still only have a 2MB cache (with the exception of 4MB blu-ray burners)?

It seems like every 6 months to a year company x puts out a slightly faster drive but the cache never seems to increase.

Burning a DVD at 1x is 1.32MB/s, CD at 1x 150KB/s, and Blu-ray 4.5MB/s so to me wouldn't it be logical to increase the cache? I mean burning a DVD at 2x would saturate the cache wouldn't it?

or am I looking at this all wrong and cache has more to do with reading discs? Even if that was the case it seems to make since to increase the cache still to reduce install times for just about anything that requires a disc.

 

[Hacp]

You know what would be really great? If they ahd 5gb chches for Optical disks. Then you could run a disk and only need to spin it initially. It would only add 10 dollars to the cost of the drive, assuming 2 dollars per gb. Would never happen though. Its too good of an idea.

 

[Quiksilver]

Right, less sarcasm....

Look hard drives are up to 64MB cache and even the bare minimum cheap drives have at least 8MB.

I remember seeing several performance tests around the time hard drives switched to SATA and made changes from 2MB to 8MB cache and the difference was massive. I would suspect to say you could see the same improvements with optical drives like less noise, less spinning up/down, longer life (due to less spins), shorter install times, etc, etc.

It's been almost 10 years since then and optical drives seem rather stagnant with the exception of them finally adopting SATA there read/write speeds increasing.

If it's about pricing, well let's just take a gander at some hard drives...

16MB VS 32MB
WD 640GB Black 32MB Cache - $75
WD 640GB Blue 16MB Cache - $70

Unless the platters are different the only difference between the two are the caches sizes and the cost difference is $5.

(I'd compare more but seagates server drives {es.2 line} are way more expensive than the consumer counterpart).

 

[pjkenned]

So the reason you have cache in hard drives is typically because you want to buffer writes to a mechanical drive. That lets you spend more time in sequential mode rather than seeking all the time.

For a burner you are typically writing from an ISO, or another set of files you know about before the burn (excluding RW here for a sec). That lets the drive write in a more or less sequential manner, and you aren't reading from an optical drive while it is simultaneously writing like you do with a hard drive. The buffers on optical drives tend to help the burners have data if your system hits 100% CPU utilization for a split second. This was much more important in the IDE days where the CPU was figuring out what to burn and then controlling the IDE channel to get the data from the source, and then to the optical media. You could start a "high priority" thread that ate 100% of a single CPU core on an IDE channel with no buffer underrun and make coasters reliably years ago. If you have heard of Plextor, their SCSI CD-R drives were less susceptible to this, and therefore they became known for quality (I had a HP SCSI burner, but was jealous until I got my own.)

RW drives... well let's face it. If you are using a RW drive as read/write storage, you don't care about your performance enough to get a USB flash drive anyway

Hope that helped.

 

[Quiksilver]

It clears up how it works when it comes to writing, but does the cache have any affect on reading?

 

[pjkenned]

Off optical media? You still have to read the data from the physical media. Sure you could do something like how high-end storage does SSD + BB NVRAM caching of SATA stored data for performance... but it would be cost prohibitive. Usage models aren't there for optical media.