Just curious if someone would like to stick this on the MPLUG wiki as a
ATA/IDE vs SCSI thing under the hardware section (since I just noticed
there is one). Someone commented that they liked my explaination.
--MonMotha
MonMotha wrote:
This is true. In terms of raw I/O speed, IDE drives have caught up with
SCSI. The reason? The bus is no longer the bottleneck. Even the best
of SCSI drives would have trouble saturating a 100MB/sec bus (though
SCSI is 160). If all you need is raw I/O speed (which is a good chunk
of what your average single user desktop will be working with,
especially if they're doing a lot of multimedia), IDE drives are a great
choice (especialy combined with a software RAID solution, such as the
Linux software RAID or some of the software "RAID" cards that are now
out for the 'dozers).
SCSI shows it's strength in Tagged Command Queueing. Unlike IDE
devices, SCSI drives can work on more than one command at the same time,
queueing them up in the best way possible. For example, an IDE system
where a person wants to simultaneously (quicker than a single seek on
the drive) pull information from 10 places on the disk will have to do
them in the order the system says. With SCSI, the system can send all
10 (or usually 9) requests in quick succession, and the drive will
service them in the best way possible, minimizing redundant seeking,
serving out of cache when possible (often even during a seek for the
next command in the queue), etc. In multiuser environments, this can
give SCSI a HUGE advantage over IDE. SCSI drives also tend to have
lower seek times, often due to smaller platter sizes rotating at
significantly faster speeds (15,000 RPM vs. 7200 or even 5400 RPM). This
is also the reason SCSI drives tend to have smaller capacity as compared
to IDE drives while still being expensive. The same "technology" has to
be used to pack all those bits into a small space, but the overall space
is smaller (many SCSI drives could almost fit their platters into 2.5"
laptop HDD enclosures, see fujisu specs on platter size). These lower
seek times also help performance in multiuser environments.
Also, though this is not as much of a deal with UDMA IDE, IDE uses the
CPU for some of it's processing. The same things are done on SCSI on
the dedicated controller and onboard the drive itself.
Conclusion: Don't assume SCSI is better, but don't assume raw I/O
bandwidth is the only measure of a hard drive.
--MonMotha
R. Scott Belford wrote:
If you intend to record most or all of the traffic moving over your
network, you need to spend as much time thinking about your disk
subsystem as your processor and Ethernet card. Last year Sandstorm
spent several months comparing IDE drives with the UDMA100 interface
to SCSI LVD-160 drives. We also explored a variety of RAID systems.
The conclusion: today's IDE drives are significantly faster than SCSI
drives costing two or three times more per gigabyte stored.
This is not the result we were expecting, and it goes directly against
the conventional wisdom that says SCSI is inherently better than IDE.
Nevertheless, it does seem to be the ugly truth, at least for
straightforward read/write tests in a single-user environment.
Although we saw the highest performance with a hardware-based RAID 5
system manufactured by _Advanced Computer & Network Corporation_, we
saw nearly the same performance with a RAID 5 system based on the
_3Ware Escalade 7000_ RAID controller.
from an article about network data capture at
http://www.oreillynet.com/lpt/a//network/2002/04/26/nettap.html
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