HDD Speed Question

What you found is normal. The 1.5 Gb/s spec is the MAXIMUM data transfer rate for a short burst. But for real sustained average transfer rates, you will get much lower. Whether 70 MB/s (560 Mb/s) is exactly right I can't say for sure, but I do know it will not come close to 1.5 Gb/s for average sustained transfer rate.

This is why some people say the difference between SATA at SATA II is meaningless when it comes to speed.

Thanks for your help. Now the things are becoming more clear.

I read in other forums that there are much higher speed hdds on the market with 120 MB/s or so (like Samsung F1 or WD6400AAKS) . I'm looking forward of buyng a new hdd (or hdds, from what I heared it seems that 2 hdds in raid0 would be the perfect speed choice) , so what should I chose for best speed.

2 HDD's in RAID0 may be a little faster because of seek speeds, but there are risks also.

The fast speeds quoted on SATA and SATA II systems are maximum transfer burst speeds - same for almost any other speed spec you'll see. But you also will see specs for Seek Time, which many discuss in terms of the related item, rotational speed. When the OS issues a request for a specific file, and once it knows where on the disk it is located, there are two operations to complete before the data transfer can start. One is to move the heads to the right cylinder position; the other is to wait for the disk to turn under the head until the correct sector comes by. So there are specs for track-to-track time, and specs for rotational speed. In the latter case, you'll see people talking about 10,000 rpm or more as better than 7,200 rpm, or even the slower 5,400 rpm units. These initial operations take significant time before the data transfer starts. Now, if the file involved is moderately large, it is likely that most of it will be on that same disk area in sequential sectors, and it'll all be read into the drive's buffer RAM during the first disk revolution, so the overall total time is affected to some extent by the initial operations. But if it's a very small file, MOST of the time is from the initial stuff, so it slows down the average transfer rate. On the other hand, for a very large file this seeking process may have to be repeated to find the rest of the file on a different cylinder.

In a RAID0 system, the file is written in one-sector pieces to two alternating disks. So, as the data from the first disk is being moved, the heads of the second disk are getting lined up. By the time the second chunk is needed, some of the seeking process is done; the alternating process continues. This speeds up the average data transfer rate.

The risk is that EVERY file has half of its data on one drive, and the rest on the other. BOTH drives are necessary, or the file is useless and corrupted. If either drive fails completely, ALL of your files are gone totally. If only a part of one drive fails, all of the files using that part are gone. Now, that's similar to the risk with any HDD. But we now are dealing with the probability that one out of two drives could fail, as opposed to the probability that only one drive fails. The probability of a one-out-of-two failure is double the single-drive case. So going to RAID0 doubles your chances of losing some or all of your files. Now, you might be prepared to take that chance, especially if you are devoted to doing good backups or something. And doubling your risk on a small risk, anyway, might be OK with you. But that's your decision to make - whether the improvement in file access speed is worth the increased risk of disaster.

Nice explanation.Now I know how a hdd works too  . As for the raid0, I'll have to think about it. I heard from my local PC seller that a guy was trying to make some hdd work on raid and managed to "fry" them both doing so.(Is there such risk?) The exact fraze was : "The guy played with some of my hdds, trying to put them in raid but he ended by broking them". I alway thaught that raid0 is just a BIOS on/off switch...so are there any particular setting that I must put so I don't damage anything ? (maybe you can give me a good tutorial link).

Also I see there are lots of RAID types. Wich is the best speed solution in your opinion? If I put more than 2 hdds in raid0, would that speed up seeking even higher (or insignificant ? ).Thanks again