Originally Posted by PobjoySpecial
Are you suggesting the full sequential write speed is available?
A single layer Blu Ray will peak ~45-54MBps in a 12x drive, with a dual layer Blu Ray peaking ~35MBps. Every movie I've ripped followed the same pattern. It started out slow (1-3x), ramped up to its peak (8-12x) and tapered off at the end. Most movies are the same length (~1h30m
), so it stands to reason that many will peak around the same time.
No, I did not say (and do not say) that the peak sequential write speed of an HDD will be reached (in aggregate) when you are writing three streams to an HDD. However, the aggregate speed is often only a little worse if the three streams are each sequential and using chunk sizes of 128KiB or larger. To put a number on it, if you have an HDD capable of a peak sequential speed of 100MB/s, I would expect it to be capable of at least 60-70MB/s when writing 3 large sequential streams.
As for your blu-ray throughput estimate, you are quoting unrealistic numbers in my experience. Yes, the maximum allowed (by blu-ray spec) 1X throughput of a blu-ray is 6.75MB/s (54Mbps), and a single-layer 12X reader could theoretically hit 12 times that, which is 81MB/s. But in reality, I've never seen a single blu-ray exceed 50MB/s peak speed, and yes, I do have a drive capable of 12X single-layer ripping. Besides, single-layer discs are rare, and the peak speed is at the end, not the middle like dual-layer discs.
For dual-layer discs, the fastest drives can rip at 8X, but again, I have never seen the theoretical maximum of 54MB/s (=8x6.75). Typical peaks are in the low 30MB/s range, and I have never seen over 40MB/s for one dual-layer blu-ray. And, of course, those are peak speeds, which are only achieved for a couple minutes in the middle of a dual-layer blu-ray rip. All the dual-layer discs that I have seen have the data at the outer edges of the disc (the unused space is always the inner tracks of the disc), equally divided between each layer, and the stream starts at the inner portion, so as you say, the speed gradually goes up, hits a peak at the outer edge of the disc on the first layer, then switches to the second layer and gradually slows down as it reads towards the inner portion of the disc on the second layer.
But since blu-rays movies have a variety of lengths (not just the movie length, but also the extra material included on the disc will have an effect on when the speed peaks) and a variety of bit-rates, both the peak speed and the time after ripping is started when the peak speed is reached will vary from disc to disc. And it does. In my experience of ripping 3 discs at once (and just starting them as quickly as I can type in the information for each one, so probably less than 1 minute of staggering the start times), there is no problem ripping to a single HDD and the aggregate peak throughput almost never exceeds 60-70MB/s.