Rookie said:
Is there any drawback in using a sata controller in the form of a pci card?
The plan is to disable the onboard IDE and keep the onboard sata plus the
sata card.
The computer to disk data transfers, can happen two ways. The data transfer
can be small enough, for the data to fit into the cache on the hard drive
controller. That might happen, at a significant fraction of the 150MB/sec
or 300MB/sec theoretical transfer rate of the SATA cable. (Packets on the
SATA cable have some overhead, so the actual transfer rate is less.)
Once a transaction with the disk is larger than the cache, then you'd be
limited by the head-to-platter transfer limit. On my current, cheap drives,
that media limitation is 60MB/sec near the beginning of the disk, and
40MB/sec near the end of the disk. The very latest drive (10000 RPM
Western Digital Velociraptor), can manage 119MB/sec near the beginning
of the disk, and 82MB/sec near the end of the disk. You can get that
data here (uses a popup advert).
http://www.storagereview.com/Testbed4Compare.sr
The PCI bus on a desktop computer, is a 32 bit bus running at 33MHz.
The theoretical transfer rate is 132MB/sec or so. When the burst
size and overheads are taken into account, the actual transfer rate is
110MB/sec to 120MB/sec. If you connected a Velociraptor to the
new controller card, then you'd still be able to sustain transfer
at the maximum rate. So it wouldn't be a complete loss.
Since PCI is shared, it all depends on where a disk transfer is going,
as to the impact it has. Say, for example, you purchased two SATA
controller cards, connected a Velociraptor to each card. Then,
went into Windows and transferred a 10GB file from one disk
to the other. The PCI bus has its 120MB/sec transfer limit, so
the disks would average about 60MB/sec each (one reading data,
the other writing data). In that case, the PCI bus is a bottleneck,
and is preventing full performance of your ($300 each) hard drives.
When a SATA drive is connected to the motherboard connector (preferably,
a port on the Southbridge), that uses a fatter bus connection than
PCI. On some Intel chipsets, the Northbridge to Southbridge bus is
1GB/sec, leaving room for SATA traffic (as well as hosting the PCI
bus). Connecting one Velociraptor to the Southbridge, and the
other Velociraptor to the PCI bus SATA controller card, would result
in better disk to disk performance.
So really, the only thing the PCI connection is preventing, is
bursting to cache at more than the media limited transfer rate. And
you may not be able to tell that limitation is there, from a practical
perspective.
If you had a really old computer, say a chipset where the PCI bus
is used to connect the Northbridge to the Southbridge, as well
as run all the PCI slots, then the odds of having contention for
resources would be much higher. For example, you might find that
every time you transferred files to the SATA card, that your
music player skipped a bit.
Paul
