[Pc_Support] External SATA bracket ($9), external SATA enclosure/power ($35)

[Jason Boxman]

On Wednesday 25 January 2006 18:23, Bryan J. Smith wrote:
> Jason Boxman <jasonb at edseek.com> wrote:
> > I'd heard ATA isn't as bad as it once was for slaving.
> > http://slug.archives.nks.net/List/slug.archive.0601/0196.html
> > http://slug.archives.nks.net/List/slug.archive.0601/0203.html
>
> Umm, _no_.  You have to look at the _context_ of that discussion.
>
> What the person was saying is that putting 2 ATA (hard drive) devices
> on the same ATA channel is _better_ than an ATA (hard drive) and
> ATAPI (optical drive).  Most ATAPI devices are only UltraDMA mode 2
> (8MHz DDR @ 16-bit = 33MBps), a few UltraDMA mode 4 (16MHz DDR @
> 16-bit = 66MBps) whereas most ATA devices are UltraDMA mode 5 (?MHz
> DDR/QDR? = 100MBps) or mode 6 (?MHz DDR/QDR? = 133MBps).  You either
> have to "slow down" the channel, or do constant bus resets to handle
> both signals.

That's not all that was said.  It was also discussed that having two disks on 
the same ATA cable and moving data between each disk doesn't suffer much of a 
penalty versus the source and target disks being on different ATA ports 
altogether.

> Furthermore, only *1* device is "on the channel" at a time -- be it
> the master or slave.  When you do device-to-device transfers and they
> are on the same channel, you copy to memory, change control, then
> back from memory.  ATA is _not_ SCSI, devices do _not_ talk directly.

Yes, I understand that.  So what's the practical overhead of having two ATA 
devices in UDMA mode 5 on the same port copying data amongst each other?  
What about if you had two mainboard ATA ports, with four disks, and you had 
two RAID 1 mirrors and you RAID 0 stripped them?

-- 

Jason Boxman
http://edseek.com/ - Linux and FOSS stuff