Why is SCSI faster than IDE

[downhiller80]

Access times: Surely the only difference between a SCSI drive and an IDE drive is the way that data is transmitted to the drive controller. Why then are SCSI access times so much quicker than IDE times and are there and easy tricks to speed up my access times?

Seb

 

[BA]

rotational speed. Just try and find a 15k rpm IDE drive...

 

[Sillyputty]

I guess that multi-threading has nothing to do with it. Internal tranfer rates don't hurt, either.

 

[Spook]

That, and it helps that the SCSI Controller takes on more of the processing than IDE....

 

[Vegito]

Yeap, SCSI has it's own processor... like the analogy of old graphics card...

In the old days.. the CPU process all 3D calculation.. now, you got GPUs, etc.etc..etc.. meaning most of the hard work is done on the video card so it gives your CPU more power to do other things.

SCSI processor does almost all the work thus giving your CPU more speed to do other stuff.

SCSI is design for speed = $ = power

A 15K IDE and 15K SCSI should be pretty close together but I believe when running MULTITASKING applications, multi-read/write to 4 different devices, SCSI kicks.. IDE can't do that yet.

i.e read from scsi 0 and write to scsi 1/2/3

 

[kyoshozx]

It's not the interface that makes scsi faster it's the drives. Even though Scsi is a better interface. Scsi is faster because manufacturers make there best drive in scsi only. Lets compare a 15k cheetah to the fastest ide drive which is still only 7,200 rpm. Don't expect to see a 15k ide drive in the near future.

 

[Ulysses]

SCSI isn't always faster. It's only faster if you get the latest SCSI devices, which are much more expensive than IDE.

 

[BoberFett]

By themselves, there isn't much of a difference. But the SCSI interface has things that speed it up far beyond anything IDE can do. Things such as: command qeueing, start up delay, spindle synchronization, etc.

 

[Pariah]

Your're partially correct bober. SCSI does have features that will speed it up a bit beyond IDE, but they only really effect performance in a multi drive per channel setup. Command Queueing, which some IDE drives now reportedly support, disconnect, and spindle synchronization (obviously) requires more than one drive to see any benefit. Start up delay is not a performance feature, but a have mercy on your power supply at boot up feature. In a single drive environment with similarly spec'ed drives, the IDE will perform better due to the lack of SCSI overhead. We're talking an imperceptible amount, but it is there.

SCSI has it's own CPU, only because it needs it. With busmastering and DMA, IDE CPU utilization is dead even with SCSI.

The reason SCSI performs better, as others have stated is because the drives are faster. Comparing a 7200RPM IBM 75GXP to a 15kRPM Seagate Cheetah X15 isn't exactly a fair comparison. Compare the IBM to a 7200RPM Quantum AtlasV, and the performance advantage will swing completely into the IDE drive's favor.

 

[Howard]

Also, SCSI drives usually have a lot more cache than IDE drives do. i.e. 4MB compared to 2MB.

 

[Howard]

DP

 

[Howard]

DP

 

[BoberFett]

Oops, thanks Pariah, I forgot to expand on what I was thinking. I started it saying "By themselves..." which had I finished would have said "in a single drive drive setup, SCSI has no big advantage. But step into the world of servers and SCSI will chew IDE up and spit it out."

 

[Pariah]

As long as the drive has cache, the amount is irrelevant performance wise.

That would be correct bober, multi drive SCSI setups in a server environment would soundly trounce an IDE subsystem.

 

[Mday]

oh, just go read the many arguments that exist.

i mean, all i did was read a book, and i knew scsi was the best. expensive makes me get ide.

and BA, try looking for a 10K IDE

and there are other things that make SCSI even faster.

don't forget fiber

 

[Hyper99]

It for server use only you really don't need such thing
for your personal enjoyment
It cost at least twice as much, sure get it if you don't mind
paying that much