[mdlug] Reordeing IDE drives in a system

[Dan Pritts]

On Tue, Oct 02, 2007 at 08:35:40AM -0400, Joseph C. Bender wrote:
> Dan Pritts wrote:
> 
> > On a related note, has anyone played with SATA port multipliers?

> 	Additionally, you'll limit your disk I/O greatly, because all the disks 
> will be sharing one SATA link back to the controller.  The money would 
> be better spent on a SATA JBOD or RAID board where every disk gets a 
> dedicated channel.

That's interesting.  I would expect that the port multipler would
make reasonable use of the huge bandwidth available in SATA -
375MByte/sec or 3Gb/sec.

Even with, say, 10% overhead that would still give about 340MB/sec.  

The fastest 7200rpm disk transfer rate is probably the 1G drives;
one hitachi drive says 1070Mb/sec max media transfer rate (and i
bet that includes the drive's on-disk formatting, so the sustained
transfer rate out the SATA interface is less).  So you should easily
fit two of these drives on a 3G SATA link and have headroom.

Smaller disks generally have slower transfer rates; and sometimes you 
might not want raw transfers but rather IOPS, so being able to handle
4 disks on a port multiplier could be reasonable.

I'm not saying you didn't have problems, but i wonder why.  I've
read that the linux port multipler support is immature; perhaps it
was a driver issue you ran into?

danno
--
dan pritts
danno at umich.edu
734-929-9770