<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by sonusman:
omnipotent, here are the issues to consider when choosing a hard drive type to use.
MAXIMUM SUSTAINED BURST!!!
<HR></BLOCKQUOTE>
Well, not really for digital audio, video, and other real-time data recording where you have long sustained data streams. Maximum burst rate is great for general purpose disc activity where small blocks of data are written.
The number one specification to look for is
sustained throughput at the interface and the disc surfaces, which will actually be a
*range* in megabytes or megabits per second. For example, an 18GB Quantum Atlas 10K Ultra-160 SCSI hard drive has a sustained media rate of 35MB/s up to 59MB/s. A Maxtor Diamondmax Plus 40GB drive has "up to 43MB/s" sustained media rate, according to Maxtor. The reason there is a range is because the hard drive reads and writes the fastest on the outer tracks and slower as the heads go towards the inner tracks.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
...But, for how long can it move that much data before the drive needs a little break? That is where Maximum Sustained Burst specs come into play.<HR></BLOCKQUOTE>
This is where
thermal recalibration comes into play -- when the drive momentarily stops
writing to perform a quick little recalibration of head positioning as the heads heat up from writing. Drives designed to write continuously without going into thermal recalibration mode won't have this problem. Other designs that allow for thermal recalibration will have large enough buffers to buffer data while the drive's not writing. These drives usually get the "A/V" moniker.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
Not only are there SCSI and IDE hard drives, but there are different hard drive speeds that affect performance. Currently, IDE as far as I know only goes up to 7200rpm's. SCSI on the other hand has drives that spin at 10,000rpm's. So, in either choice of hard drive types, get the fastest rpm's, but don't even invest a dime into the standard old 5400rpm disks.<HR></BLOCKQUOTE>
It's certainly possible to have a 5400 RPM drive that's capable of a higher sustained read/write throughput than a 7200 RPM drive. For the most part, it all comes down to how many MB per platter these drives have (i.e. -- the data density).
Where RPMs matter the most is in access time, because the heads in a higher RPM drive can get back to a certain sector on any track faster than the heads in a lower RPM drive can. But, for the most part, higher RPM drives have also meant higher overall throughput. There is a limit (frequency response) on just how fast hard drive heads can read/write, so the designers have to take this into account when they are coming up with track density / RPM design targets.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
Now, hard drives are still not all created equal, even if you get the newest ATA66 7200rpm, or a Ultrawide2 SCSI. I talked about maximum sustained burst's, and that has a lot to do with whether the drive is a LVD drive or not. LVD drives do not have the same thermal issues that regular non-LVD drives do, so they spin continuously and just won't stop at all.
<HR></BLOCKQUOTE>
Well, for one thing, if you're in the market for a new SCSI hard drive, nobody is making hard drives less than Ultra2 (80 MB/s). You can still find new/old stock Wide/Ultra (40 MB/s) and maybe some Wide/Fast (20 MB/s) drives, but you really need to search hard for those nowadays. In fact, Ultra2 is mostly out the door with Ultra-160 (160 MB/s) taking over completely. After a while we'll start to see drives with Ultra-320 interfaces, then Ultra-640 SCSI.
As for ATA5/UDMA-66 being the top interface in the ATA/IDE world, UDMA-100 is just around the proverbial corner. Then there's serial ATA on down the road aways at 1.6 Gb/s (200 MB/s).
The big performance differences between ATA drives and SCSI drives is the way the interface works. An ATA interface processes commands in a very simplistic way -- sequentially. SCSI on the other hand can perform command queuing which is much more efficient in a multi-tasking and/or multi-user environment.
Why do SCSI drives cost more than ATA drives? It's mostly the electronics on the hard drive and the drive mechanism's spindles which are designed for high temperature and 24/7 operation.
Are SCSI drives a good investment? Maybe YES, maybe NO. For certain applications -- like digital audio workstations where you need a certain level of performance and reliability -- it can be a good investment. If you can prove that you NEED a certain level of throughput OR reliability, then yes, SCSI is the way to go. Otherwise, you are wasting your money.
Q: What the hell do I have? A: A pair of IBM 9GB Ultra2 SCSI hard drives (soon to be replaced by a pair of Quantum 18GB Ultra-160 drives) running as a disc array in RAID-0 mode. Go figure.
