Yeah - the more reading I'm doing - the more I'm finding out. Alledgelly the Western Digial Raptor drives implement a version of ATA-4 Tagged Queing which allows reordering of commands. Some controllers support this. The 3ware docs say that the controller support both reordering on the controller and to the drive. *shrug*
This of course is all supposed to go away with SATA II which as NCQ, Native Command Queueing. Of course the 3ware controllers don't support SATA II, but a few other do, and I'm sure 3ware will come out with a controller that does. Alex Turner netEconomist On 06 Apr 2005 23:00:54 -0400, Greg Stark <[EMAIL PROTECTED]> wrote: > > Alex Turner <[EMAIL PROTECTED]> writes: > > > SATA gives each drive it's own channel, but you have to share in SCSI. > > A SATA controller typicaly can do 3Gb/sec (384MB/sec) per drive, but > > SCSI can only do 320MB/sec across the entire array. > > SCSI controllers often have separate channels for each device too. > > In any case the issue with the IDE protocol is that fundamentally you can only > have a single command pending. SCSI can have many commands pending. This is > especially important for a database like postgres that may be busy committing > one transaction while another is trying to read. Having several commands > queued on the drive gives it a chance to execute any that are "on the way" to > the committing transaction. > > However I'm under the impression that 3ware has largely solved this problem. > Also, if you save a few dollars and can afford one additional drive that > additional drive may improve your array speed enough to overcome that > inefficiency. > > -- > greg > > ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org