Question About IDE Raid

[Kurt]

Originally posted by rugger
I think I know why your raid is performing so poorly. It may have something to do with PCI performance.

If your PCI bus cannot keep up with the drives, then the drives will be unable to read the sectors as they pass under the drive heads. This will end up forcing the drives to make extra revolutions to read sectors and serious STR performance problems result from that.

With 2 modern drives, the STR rate of your RAID array would range between 120 and 80megabytes per second, which many PCI chipsets simply can't handle.

Given that your burst rate on your RAID array was only 70megabytes per sec, this does sound like the problem. I had the same problem with bandwidth when I connected a 7200.7 drive to an old LX motherboard and ATA-33.

I would simply run them as 2 separate drives.

One more stupid question, do you have both drives on the ITE raid controller their own channels ... ie, are the both on different cables?

I second that. There's was an nice and easy article about that, published not long ago on one of the many hardware sites, alas I couldn't find it again

A good way to up the speed of the system could be to buy a nice WD Raptor 74GB 10K rpm and sell the other Samsung drives or use them as storage...

[cbman]

Now I have a question... the theoretical max transfer rate for the PCI bus is 133MB/s - and the STR of these two drives would be around 80 or so (Just a guess)

The only other PCI Device I have in the system is the Soundblaster Audigy card... shouldn't there be enough room on the bus for it to transfer data at the full rate or is it the DMA Burst Rates that are causing the problem because that would be close to 160 MB/s

If thats the case then changing it to PIO mode and disabling DMA should have an impact upon the performance... or setting the DMA transfer rate to a lower spec say ATA66.

Just some ideas I have...

[Ribbit]

You'll never actually get 133MB/s over the PCI bus. There's wait states, protocol overhead, and lousy chipset design to take into account (and lots more, I'm sure). 80MB/s is actually a good real-world figure.

Oh, and I wouldn't change to PIO mode - your CPU usage will skyrocket.

[cbman]

Well if you look at it you can see from the JPG's that the CPU usage is around 20% which is still high with DMA enabled... it should be more like 5-10% at the most.

[Wombat]

Speaking as a RAID0 user, I wouldn't do it again. I just didn't get any real extra performance. I think there's a setting in WinXP that can be tweaked, but whatever.
I RAIDed to have a very large partition and a speed increase. The former I can work around, and the latter I didn't get. Whenever I get another hard drive, I'm going to use it first to un-stripe my Maxtors.

[rugger]

Originally posted by cbman


If thats the case then changing it to PIO mode and disabling DMA should have an impact upon the performance... or setting the DMA transfer rate to a lower spec say ATA66.

You will get the same problem. Any time that your computer is unable to accept the full performance of the RAID array you will get serious performance degredation due to the sector skipping I mentioned above

[cbman]

Ah well... I'm still playing around with it... I'm probably going to unraid it and deal with it... until I find a better solution...

What a pain in the ass though... Good thing I haven't started my projects yet...

[rugger]

I am at a loss as to what projects would need 120mbit per second STR?

Even work that benefits from's high STR ussually is better done with 2 separate drives, with the source on one and the destination on the other.

[SuRGV]

I was so excited about RAID-0 performance from reading comments on the Net. The reality was a big disapointment after spending some $$$$ for a RAID card. No speed improvemnts felt at all except in benchmark graphs.

I'm now on RAID-1 for data security.

[cbman]

My Friend Wants To Start Playing Around With Video Editing With His New DV Camcorder... I was going to Swap Out The Maxtor and Make it A Backup Drive and get another WD drive to Pair up with the one I have to Make a Second Set... That Way I would have had 2 separate Arrays to make it like you said... have one for the source and one for the output... but its not going to work with raid... so its all moot... ah well... I'll just do it on single drives and deal with it...

[Kurt]

Originally posted by SuRGV
I was so excited about RAID-0 performance from reading comments on the Net. The reality was a big disapointment after spending some $$$$ for a RAID card. No speed improvemnts felt at all except in benchmark graphs.

I'm now on RAID-1 for data security.

The problem is not RAID0, it's your PCI bus. If you invest in a mainboard with a 64bit PCI bus and a 64bit RAID controller, you'll get the speed increase.

[dZeus]

lol... nope.

Read up on the RAID performance comparison article on storagereview.

[cbman]

Hey DZeus... do you have a link for that article... sounds like an interesting read.

Thanks

[dZeus]

https://www.storagereview.com

[Kurt]

you mean:

The Escalade 7000 Series Revisited: 3Ware's Escalade 7450

It's a November 2001 article.

Here's where the fun begins:

64-bit PCI vs. 32-bit PCI - When Does It Matter?

Also:

"With the Escalade 7450 achieving 116MB/sec of STR performance in the testbed, there wasn't much room for improvement in the 370DE6 system. Each Diamondmax 80 used for testing can sustain just under 30MB/sec - four DM80's, therefore, can't do much better than 116MB/sec . Indeed, the score of 118MB/sec achieved in the 370DE6 system is clearly a limitation of the drives themselves as opposed to the 7450.

I wish they'd redo it with _new_ drives.