On Sun, Feb 16, 2003 at 03:26:33PM +1100, Russell wrote: > What's better about scsi drives? I saw an old scsi controller card > at a PC meet today.
SCSI is much more efficient than IDE as it does not force the processor to hang around waiting for commands to complete. So you don't get a massive and unproductive CPU usage hit when doing disk I/O. You know how the system gets dead slow when you're burning a CD? That's not because burning CDs intrinsically needs lots of CPU, it's because the IDE interface does. This is why, when systems were a lot slower and CD writers were just coming out, they were all SCSI, and such systems are better for burning if you have a SCSI hard drive too. If your SCSI card has an LED indicating bus activity, and the SCSI hard drive has an LED indicating drive activity, it is interesting to see that unlike similar LEDs on IDE, they are often not both on at the same time. The bus activity LED flashes, then the drive LED comes on, then the bus activity LED flashes again. While there is nothing moving on the bus, the CPU can deal with other stuff. With IDE, it's waiting for the bus. The result is that a system with SCSI drives tends to be more responsive than a similar system with faster IDE drives! But SCSI performance is way ahead of IDE; you can't buy a new drive slower than 160Mb/s and 10,000rpm. So don't get too old a SCSI card. Basically you want one with at least a 68-pin, and preferably an 80-pin, SCSI internal connector, depending on the age of your system. (This is a gross simplififcation!) The old 50-pin versions are really too slow to be useful these days, and the newer ones usually support 50-pin as well. Other nice things about SCSI drives: - fault remapping: if a sector starts becoming dodgy the drive will save the data elsewhere before it gets too bad to read at all, and mark the sector in a defect list, without the computer having to know anything about it. - CHS/LBA: SCSI has always worked in terms of LBA, so you get far less in the way of problems when moving drives from one machine to another, or dual-booting, as a result of CHS translation algorithms changing and becoming inconsistent with the partition table - problems like unbootable systems, unmountable partitions, and in the dual-boot case, Windoze scribbling junk into your Linux partitions. - drive identity: the drive identity setting mechanism is consistent between different drives, and it works. You don't get problems as with some combinations of IDE devices where you have to play games with the master/slave/cable select/funny four-option jumper set jumpers to get the drives to work happily. - second-hand prices: although new SCSI drives are expensive, the fact that not many people have SCSI cards means that second-hand SCSI drives are hard to sell, and tend to be cheaper than similar-size IDE drives. They are also faster than similar-age IDE drives. Pigeon -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
