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CPU power or HDD speed?

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April 12, 2002 8:53:58 PM

Ok, I found that the low hdtach #'s I was getting were cause the block size was all too big. If I set it to 2KB, I get max of 81MB/s, and constant stream of 51MB/s. This uses 19.5% CPU. If I set it to 4KB, I get 80MB/s max, and 50MB/s constant, w/ 17.2% CPU utilized. Which one would u choose?

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April 12, 2002 10:15:18 PM

I would be tring to get the utilisation down a minimum. Lower than either of those values. In a couple of tests I did right now, I had 10.3% & 12% utilisation.

Speed may be important, but not at the cost of any other part IMHO. My CPU is a PIII GHZ, so not that much different from your own one. Okay not <b>that</b> much. :smile:

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April 12, 2002 11:16:46 PM

I would save the 2.3% rather then the 1 meg, but that is just me. Out of curiousity what controller are you using for your hard disk, that CPU rate seems rather high....

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April 12, 2002 11:40:33 PM

Well, I found that w/ a 8KB block size, I get transfer rates of around 82MB/s, and utilization if 17.6% There were a few background apps running though.......
Also, I may be getting a XP2100+ soon, so I'm cool w/ that cpu utilization. And quite honestly, when I use it, winxp says cpu is idle, and 1% is used. Maybe HDtach or something. I can get utlization to 9%, but that means transfer rates of 35MB/s, which sucks. I'd rather have basically minimum of 51MB/s, my mid transfers being in teh high 60's, and about 30% in the 80MB/s.

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April 12, 2002 11:41:00 PM

This is w/ a TX2000 controller.

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April 13, 2002 1:22:16 AM

IDE software raid explains the cpu usage =)
Still I get less then that on my built in KG7-RAID, although I have not tested it since I added new drives cuz I have em mirrored at the moment and have SCSI stripped =)

Jesus saves, but Mario scores!!!
April 13, 2002 5:14:12 PM

Some will call Promise, Iwill, etc. controllers "software RAID," but this is only partially true. Most people that use this term use it from the sense of software modems (or Winmodems). But software modems require software to be installed to function - you can't use them from a DOS prompt with no drivers loaded. IDE RAID devices do not suffer from this restriction - they can be used without drivers from DOS - they actually perform the work in hardware. The reason many people relate them to software modems is that they use the processor to do the majority of the work for them instead of using an onboard (PCI Card) processor. This is not "software RAID," it is "processor-dependant RAID." There is a big difference - you can't boot from software RAID. Software RAID is available in Win NT/2K/XP and some versions of Linux/Unix if you are interested. IDE RAID uses the processor in the same way that a standard mobo IDE controller uses the processor. Many peripheral cards (video, HD controllers, serial ports, etc.) used this model for the first 20 years of the existance of the PC. So, these devices, while processor-dependant, are not software based.

Back to the question - My preference is more HDD speed for my servers and less CPU usage for my workstations.

I thought a thought, but the thought I thought wasn't the thought I thought I had thought.
April 13, 2002 7:49:04 PM

That concept can be debated as well. Just because the ide raid card contains a bios with a set of instructions telling your OS that it is a raid controller and then offloading the processing requirements to the CPU does not make it "hardware" either. Call it a morph if you will but it is a far cry from a hardware controller. Setup a software stripe in 2k or xp and compare it cpu utilization wise to one of these controllers and you will find that the results are very simular. Just like winmodems all have various degrees to which they tax the CPU, the same is true for the vast majority of software based raid cards.

It's not what they tell you, its what they don't tell you!
April 14, 2002 12:56:35 AM

It doesn't have to tell the OS anything. My point was simply that they don't actually require OS driver software to function - these are loaded later. They <i>are</i> hardware controllers - just like the onboard IDE and parallel ports are hardware - they simply use the system CPU - just like onboard controllers. The big difference is that the RAID controllers in question contain the software required on board - they just have less hardware because they use the system CPU instead of a separate integrated one. They do this from POST - not after OS load. It must be said that nearly all (99%) of hardware could be called a software peripheral as they all contain software in flash or eprom, etc.) Yes, these controllers require drivers to function under some OSes, but so do all "hardware" SCSI and RAID controllers. The difference is that SCSI and some RAID controllers have onboard processors and use almost no CPU. In some cases the IDE RAID controller does even use optimized software to perform some of the RAID functions - this is for performance under a specific OS and these optimizations are not required for the card to function. Yes, software striping in XP or 2K has similar CPU utilization to these controllers - they are using the same CPU. But, you can't boot from software RAID, because the array doesn't exist until the OS is loaded - this is software RAID.

Thus, most current consumer oriented IDE RAID controllers are a hybrid - hardware based, but system CPU dependant.

I thought a thought, but the thought I thought wasn't the thought I thought I had thought.
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