IDE RAID Setup Question



I have an ABIT TH7II-RAID Motherboard. It has a Highpoint HPT370 RAID chip with 2 channels.

I have 4 drives in my box, 2-20 gig and 2-60gig. I'm using the 2 20's as a mirrored array for the boot disk and the 2 60's as a stripped array for data. It's already setup with the 2 20's on one channel and the 2 60's on the other channel. All drives are configured as cable select. I read somewhere (maybe here) that you should put disks from the same array on different channels. Should I switch the 2 slave drives to the other channel?

To clarify:
Current config:
Primary Channel Master 20 gig (array 1 drive c: )
Primary Channel Slave 20 gig (array 1 drive c: )
Secondary Channel Master 60 gig (array 0 drive d: )
Secondary Channel Slave 60 gig (array 0 drive d: )

Proposed config:
Primary Channel Master 20 gig (array 1 drive c: )
Primary Channel Slave 60 gig (array 0 drive d: )
Secondary Channel Master 20 gig (array 1 drive c: )
Secondary Channel Slave 60 gig (array 0 drive d: )

Assuming the proposed config is what is suggested, can I just swap 2 of the drives and go or will I need to rebuild both arrays? I assume that the array information is stored on the drive itself. If I have to redo the arrays, is the performance increase worth the hassle?

I did a quick speed test on the 2 arrays as they are currently configured. The results are as follows:


Thanks for any help!



You are correct

Moving the set drives to separate channels should increase your performance and may very well be worth the effort. (The amount depends on the size and number of files being transferred when benchmarking). It is ideal to have each drive in the same set on a separate channel so that it has the full bandwidth of the IDE channel for its use. If your drives can sustain a tranfer rate of 66MB/sec (DMA66) and you put them both on the same channel, they would only effectively be 33/mb per sec due to the bandwidth limit on the channel, whereas if each was on its own separate channel, it would have the full 66 of each channel to work with. Now, its very unlikely thaht most drives can sustain their theoretical limit for any reasonable length of time, but still it would be ideal to keep them on their own channel.
As for just swapping the drives, I'm afraid the arryas will need to be rebuilt from scratch. I understand that their may be a way using a third drive to mirror them so that a new set can be built, but I'm not familiar with that. Perhaps someone else here has a suggestion for that. Another option may be that you can use Symantec Ghost to image the array and then ghost it back on to the new array so can completely maintain your current setup and it will take less than ana hour most likely to image and re-image your drives versus hours of re-installing. I have not used ghost on a raid array in IDE before but I think this would work.



Since the HPT370 Controller can support 100MB/sec/channel, I would assume that the maximum thoughput on a striped array would be 200MB/sec when the drives are on separate channels, correct?

Does ghost work on an IDE raid array when booted to DOS?


That's correct. I was thinking of mine on my KT7 raid where I have 2 dma 66 drives, but yeah exactly, you can get (in theory) 200mb/sec transfer rate that way since each channel can handle that much. Most drives just can't do that kind of output (100mb/sec) except for small bursts, but it could happen :). I know that if I boot from a floppy to a DOS prompt, that I see (in my case) one 12gig drive even though it is two 6gig drives in a raid 0 config. So, I assume that ghost will see it as one drive as well. I seem to remember reading somewhere while researching setting up my KT7 raid, that the HPT Bios supports DOS without additional drivers so ghost should work. I hope so as that will save you a lot of hassle.


It would be nice to have 200MB/s throughput but the PCI bus is limited to 133MB/s including all the other devices on it too.

Your throughput will be substantially less anyhow as the sustained read transfer rate from each drive will be between 15MB/s and 40MB/s (given current drive capabilities-not sure what drives you have).

However, the above posts are totally correct that putting each drive on a separate channel will boost your performance as the IDE bus is not as good as we would like. Data transfers can only occur from 1 drive at a time on any Channel, so 2 drives on a single channel can only go as fast as 1 drive, under ideal conditions.


Does that remain true if the drives are not all the same? Such as a mixture of UDMA 3,4,5,6 ?


these are the transfer rates of the different DMA standards:

UDMA 3 = 33MB/s
UDMA 4 = 66MB/s
UDMA 5 = 100MB/s (supposedly)
UDMA 6 = 133MB/s (supposedly)

The DMA speed isnt the main thing that dictates the drives speed but it can have an effect on regularly used files (which could also be cached in ram too)

but bear in mind that all of the above is burst transfer rates.
Many drives cant transfer above 30MB/s sustained even though they may be UDMA100+ Drives (Burst of 100MB+/s), so for the most part, no it doesnt matter if they are UDMA33 or UDMA133 drives, they will almost perform the same

Please note that UDMA33 drives are in general a lot older and are likely to be slower as they are slower technology, but the basic principle holds.

If you are comparing UDMA66 to UDMA100/133 drives, you will pretty much see the same performance for the same speed/Size drives (ie 7200rpm 60GB).

y'know it was tough reading that after a few beers.

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