ATA 133 Raid and WD 120 GB Drives

[sapiens74 0]

DO any of you know, if I were to use 3 ATA 100 Drives, could it be possible to use the extra bandwidth on an ATA 133 controller, of would it peak at 100?

[Brian Frank 0]

ATA133 has been shown to amount to jack in a performance increase. It's there, but the current ATA drives just can't saturate it. Honestly, you can get away with ATA66 cables and not know a thing. Even in RAID (assuming you're doing the smart thing and having each drive on it's own channel) you still won't fill up the available bandwith.

[sapiens74 0]

SO I i put 3 drives each capable of sustained rates of 50mb on thier own, in a 3 drive stripe, it won't max out the controller?

[zen69x 0]

first, there are no IDE drives capable of 50MB/s sustained transfer. The WD w/ 8MB cache is close, but not quite there yet.

 

anyhow...look at it this way... each channel is limited to a maximum rate of it's supported protocol... i.e. ATA33=33MB/s 66=66 etc... all minus a few MB/s due to overhead. You will set them up so that each has it's own channel due to IDE having only 1 device active per channel at any given time. So, no the controller won't be maxed out.

 

The problem you will see however is that all IDE interfaces connect to the PCI bus. And more than likely you will have a 32bit 33Mhz PCI bus... the bandwidth limit on the bus is 133MB/s. Of course this bandwidth is shared also w/ any other PCI devices in your system... sound card, NIC, etc. This is mainly why ATA133 is a real waste of time, except to support HDD >137GB. However, if you have 64bit 33Mhz or 66Mhz PCI bus, then you have nothing to worry about... if your IDE controller card is rated to work on that type of PCI bus. I would venture to guess though that if you have a motherboard w/ a 64bit PCI bus... you're probably running SCSI hard drives though.

[sapiens74 0]

2 channel ata 133 raid card. 1 channel with 2 drives on it that only support ata 100. So that one channel at max can transer 100 mb per sec. whereas the other channel will have 1 drive on it, that can possibly do 50 mb on its own. So that's a total of about 150, not counting the fact that they are striped.

[Brian Frank 0]

Also consider that since you only have two channels, that 3rd one may not be accessible all the time, slowing down the array, and thus defeating the purpose of RAID 0.

[sapiens74 0]

still doesnt answer my question. Will it come close to maxing out the card? I can almost max out my ata 100 raid now with 2 drives, maxtors at that

[zen69x 0]

ok, maybe you didn't read my post all the way though... I said, no you won't be maxing out the card. Your bottleneck is the PCI bus.

 

First, you are not maxing out any ATA100 RAID 0 array. the most SUSTAINED transfer rate on *any* IDE drive right now is slightly less than 44MB/s. Yes, that SUSTAINED rate will be about double, 88MB/s but you are only using ~1/2 of the total pipe available... 100MB/s per channel = 200MB/s, which you CAN'T use anyway due to PCI bus constraints. ...BTW, I don't much care about burst rates on the drives cuz you aren't going to be retrieving all that much data from a hard drives 2MB cache to really see a difference.

 

Secondly as I said and Brian Frank reinterated, since you have 2 drives on one channel and 1 on another, you can only have 2 drives active in the RAID array at any given moment due to IDE ONLY being able to communicate with 1 device on a channel at any given time... so it will only offer max the same bandwidth as a 2 drive array, maybe less due to the overhead in switching devices on the channel w/ two drives.

 

Finally, again as previously stated, the bandwidth on the PCI bus is shared... you start out w/ 133MB/s theoretically, and that is shared amongst the IDE controller, NIC, sound card, USB, and any other PCI devices you have. Think that most realistically you may expect is 100MB/s. So I don't care if you have a U320 SCSI controller even, you STILL have to go through the PCI bus for anything meaningful to happen and that is where you are bottlenecked.

[sapiens74 0]

Ok I didnt ask for the PCI specs which I already know whould be the bottleneck. what I asked is if that would max the card out. Whether the card can push data through the pci bus at that rate is irrelevant.

 

Btw the WD can sustain a rate of 49mb/s on its own.

 

I just didn't want to waste money on more then 2

[Brian Frank 0]

Since the card is as 33MHz/32-bit PCI card, and you're using IDE devices, you will not constantly max out the card. Like mentioned previously, the bursts rates will hit 100MB/s, and that is the only time you can come close to maxing out the card is during burst transfer rates. Since IDE devices cannot access more than 1 device at a time, regardless of any RAID array, you will be using only 2 drives at once, tops. Adding the third drive won't max out the card because the card can't access more than 2 drives anyway.