SCSI bandwidth sharing question

[dajo]

Hello,

I have a Cheetah 15.3K (18.1GB) on an LSI Logic card. I found a good price on a WDC 9.1 10k SCSI.

Is sharing that on the same card is going to slow my Cheetah down or will I not even notice it?

Thanks!

 

[Peter]

Hardly. SCSI HDDs release the bus between command reception and data transmission. This has two effects - the bus is never hogged in an idle state, and the actual data transmission is always from the drive's internal buffers, thus taking place at the full interface rate.

So, command overhead aside, two HDDs that have peak transfer rates of around 65 and 40 MB/s still leave you with plenty headroom on an U160 channel. First thing that limits you will be the stupid 32-bit 33 MHz PCI bus at around 120 MB/s.

HOWEVER: If that WD drive uses an UW interface only not some sort of LVD (U2W or U160), then it's going to kick that SCSI channel back to UW altogether - and at 40 MB/s total bandwidth, you ARE going to be limited. If the drive uses U2W, then it'll eat twice as much bandwidth yet the other drive still operates at U160, so that wouldn't hurt.

regards, Peter