I'm not sure whether it's really worth arguing this with you or not, since it seems you think that the Apple XServe is the best thing since sliced bread (I don't have a thing against it - it looks like a really nice machine), but here goes anyways.
It's got nothing to do with Apple vs. PC or anything like that (though that wasn't really anyone's point). It does not really have much to do with Serial ATA vs SCSI interfaces either. It's mainly the fact that current top-of-the-line serial ata drives only spin at 10000RPM (the ones in Apple's XServe to my knowledge are only 7200RPM drives), while SCSI drives spin at 15000RPM. That difference in spindle speed makes a huge difference in latency, which is very important for database applications.
This link here compares the performance of 4 drives:
From these numbers, looking at disk read times, it goes from 5.6ms for the 15k to 12.1ms for the 7200rpm drive. That makes the 15k drive more than twice as fast for an average read.
You mention iTunes as your reason why SATA drives are faster than the 15K SCSI drives, but there's not much to go by there. We don't know what kind of setup they have running the operation. They could have a million Xserves running it, or just one.
I thought this would be fun to figure out. This article says that iTunes has sold over 20 million songs in around 8 months. On average, that's around 1 song download per second. Considering people aren't going to be evenly downloading songs throughout the day like that, take the peak, say they do 6 hours of this 'distributed' traffic in 1 hour, then that's around 6 songs purchased per second. If a song averages at about 6MB and the average download speed is 10KB/s, then it would take about 600 seconds for the download to complete. In each of those 600 seconds, you have 6 more people starting downloads, so that's around 3600 simultaneous downloads, downloading at a total of 36MB/s.
With 100,000+ songs at around 6MB a piece, that's at least 600GB of space needed. Triple that to be safe, so they need 2TB of space that can handle 36MB/s of sustained, random transfers. Sweet.
Man this thread has gone waaaay off topic...
Adrian
It's got nothing to do with Apple vs. PC or anything like that (though that wasn't really anyone's point). It does not really have much to do with Serial ATA vs SCSI interfaces either. It's mainly the fact that current top-of-the-line serial ata drives only spin at 10000RPM (the ones in Apple's XServe to my knowledge are only 7200RPM drives), while SCSI drives spin at 15000RPM. That difference in spindle speed makes a huge difference in latency, which is very important for database applications.
This link here compares the performance of 4 drives:
- Fujitsu MAS3735 (one of the fastest 15k scsi drives)
- Maxtor Atlas IV (one of the fastest 10k scsi drives)
- Western Digital Raptor WD740GD (one of the fastest and only 10k sata drives)
- Hitachi Deskstar 7K250 (one of the fastest 7200rpm sata drives)
From these numbers, looking at disk read times, it goes from 5.6ms for the 15k to 12.1ms for the 7200rpm drive. That makes the 15k drive more than twice as fast for an average read.
You mention iTunes as your reason why SATA drives are faster than the 15K SCSI drives, but there's not much to go by there. We don't know what kind of setup they have running the operation. They could have a million Xserves running it, or just one.
I thought this would be fun to figure out. This article says that iTunes has sold over 20 million songs in around 8 months. On average, that's around 1 song download per second. Considering people aren't going to be evenly downloading songs throughout the day like that, take the peak, say they do 6 hours of this 'distributed' traffic in 1 hour, then that's around 6 songs purchased per second. If a song averages at about 6MB and the average download speed is 10KB/s, then it would take about 600 seconds for the download to complete. In each of those 600 seconds, you have 6 more people starting downloads, so that's around 3600 simultaneous downloads, downloading at a total of 36MB/s.
With 100,000+ songs at around 6MB a piece, that's at least 600GB of space needed. Triple that to be safe, so they need 2TB of space that can handle 36MB/s of sustained, random transfers. Sweet.
Man this thread has gone waaaay off topic...
Adrian
