SATA or SCSI drives - Multiple Read/write speeds.

Lombard, David N david.n.lombard at intel.com
Tue Dec 9 10:03:12 EST 2003


From: Mark Hahn; Sent: Monday, December 08, 2003 3:18 PM
> 
> SCSI:	pro: a nice bus-based architecture which makes it easy to put
> 	many disks in one enclosure.  the bus is fast enough to
> 	support around 3-5 disks without compromising bandwidth
> 	(in fact, you'll probably saturate your PCI(x) bus(es) first
> 	if you're not careful!) 10 and 15K RPM SCSI disks are common,
> 	leading to serious advantages if your workload is
latency-dominated
> 	(mostly of small, scattered, uncachable reads, and/or
synchronous
> 	writes.)  5yr warrantees and 1.2 Mhour MTBF are very comforting.

Very big pro:  You can get much higher *sustained* bandwidth levels,
regardless of CPU load.  ATA/PATA requires CPU involvement, and
bandwidth tanks under moderate CPU load.

The highest SCSI bandwidth rates I've seen first hand are 290 MB/S for
IA32 and 380 MB/S for IPF. Both had two controllers on independent PCI-X
busses, 6 disks for IA32 and 12 for IPF in a s/w RAID-0 config.


Does SATA reduce the CPU requirement from ATA/PATA, or is it the same?
Unless it's substantially lower, you still have a system best suited for
low to moderate I/O needs.

BTW, http://www.iozone.org/ is a nice standard I/O benchmark.  But, as
mentioned earlier in this thread, app-specific benchmarking is *always*
best.

-- 
David N. Lombard

My comments represent my opinions, not those of Intel.
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