> RE: SCSI needed for best performance -
> While this is true in some cases, if you are using striping or any
> RAID level (RAID 5 for example) that splits reads and writes across
> drives, then there will be several IDE channels feeding data to the
> RAID card at a time. Two ATA100 IDE channels will accept and provide
> data faster than the PCI bus that the card is plugged into can. The
> result is that you can use cheap IDE drives and get the same
> performance as the very fastest SCSI drives.
I don't think this is generally true. For database-type applications,
even with multiple drives, throughput is usually limited by seeks
rather than data transfer rate. One of the capacity that Scsi drives
have that IDE drives don't is the ability to send multiple overlapping
transfers to the drive, which can then execute them out of order.
Firstly, it can do "escalator seeking" - sort into position on the disk
so as to minimise the number of end-to-end seeks. Secondly, it can trade
off short seeks against rotational latency, because it knows tha angular
position of the disk at any time. I found that the second feature alone
added about 25% to net performance.
Alec
--
MySQL General Mailing List
For list archives: http://lists.mysql.com/mysql
To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
