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Four 500gb hdd RAID in one pci slot

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June 22, 2010 6:11:24 PM

I have an old Fujitsu Siemens board with the 875P Intel chip. I am trying to get now a RAID controller for four 500GB WD HDD to build a two or four drive RAID 0. The board has 6 PCI slots. I already tried running the drives in a SilImage 0680 chip controller card and the second set of drives doesn't work, very slow etc. I figured the card is not capable of supporting these drives that give a total of 2TB of space. Installing two of the hard drives in a regular PCI Promise card works relatively well. I am researching the market and I can get some older RAID controllers from 3ware that will work with my four WD drives.

My question- is it better to get one 3ware controller supporting four IDE drives and install it in one pci slot, or getting two RAID controllers and installing them in two separate PCI slots, running two RAID sets in two different cards and PCI slots? By the way I tried the SilImage card with four HD previously, two 500GB ant two 250GB and worked, but since introducing the two new 500GB HDD the card or the PCI bus bottlenecked. Now would one more superior RAID controller such as the 3ware solve that problem or should I stay "safe" and get two of them just in case and install them on two PCI slots.

Cheers
Nik
June 22, 2010 6:24:55 PM

I forgot to mention that these are all IDE drives so I am buying an older controller and the RAID is for storage use only. My OS is on a WD SATA Raptor HDD attached to the MB.

Cheers
Nik
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June 22, 2010 9:59:10 PM

Bummer....

I thought that was a simple questions for people with more RAID experience, but I guess not.
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a b G Storage
June 23, 2010 12:13:29 AM

Well two cards would be better as one PCI slot could handle a theoretical maximum of about 133Mbytes/s and likely not more than 100 in the real world.

The PCI bus itself may cause a limitation as well.

If you have the drives you can go for it but I would suggest upgrading to a board with PCIe and using a zfs based raid0 or anything else.

Are you going to run freeNas or something similar?
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a b G Storage
June 23, 2010 12:47:43 AM

> My question- is it better to get one 3ware controller supporting four IDE drives and install it in one pci slot, or getting two RAID controllers and installing them in two separate PCI slots, running two RAID sets in two different cards and PCI slots?


The PCI bus only allows one device to use it at any given time,
so 2 RAID cards are not going to communicate to the CPU
any faster than a single RAID card.

The legacy PCI bus transmits 32 bits @ 33 MHz = 1,056 Mbits/sec

1,056 / 8 = ~133 MBytes/second


Anther consideration is that PCI RAID cards generally
do not support 2 of the same on the same PCI bus:
you would need to check with the manufacturer
to confirm whether or not any given card can be
"doubled-up".

Mixing brands is even less likely to inter-operate correctly.

If you can find PCI RAID cards that can double-up,
they may achieve a modicum of parallelism,
but I predict it won't be very noticeable due to
the general technological limitations of the PCI bus.

Specifically, EVEN IF you had 4 x IDE HDDs working
with 2 x RAID cards, the MAXIMUM data rate will
remain at 133 MB/second regardless, because
the PCI bus is the bottleneck with such a
configuration: I've seen this experiment done
several times, and every resulting graph tops out
at about 130 MB/second -- almost perfectly flat line!


You're better off going with a single PCI RAID card
with a good reputation. We've had much success
with the Highpoint RocketRAID PCI controllers e.g.:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Your 875 chipset should also have a few SATA ports:
you'd be better off buying one or two SATA HDDs
because they have larger caches and use PMR.

PMR allows tracks to be much closer together,
resulting in a slower decline in recording speed
from outermost to innermost tracks.

This graph demonstrates how HDDs can vary a
lot on this measure:

http://www.supremelaw.org/systems/io.tests/platter.tran...


Just remember to check the documentation,
because I believe SATA ports on the 875 chipset
defaulted at 150 MB/second, and all modern SATA
HDDs default to 300 MB/second. If you don't add a
jumper, your chipset won't recognize the faster speed.


Moral of this story: get faster SATA HDDs
because they now can be expected to exceed
100 MB/second from buffer to disk (raw data
rate directly under the read/write heads).


MRFS
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June 23, 2010 1:44:55 AM

Thank you very much Sir, you really know what you are talking about.

Unfortunately my MB has 2 SATA 150 built in and two IDE channels (4 IDE devices total), I already mentioned that my OS is installed on one WD Raptor attached to the MB and I was just looking to expend my storage for movies and other media files, so the reason for the RAID. One one of the IDE channels I have two DVD burners.

I was thinking to purchase one of this cards http://www.newegg.com/product/product.aspx?item=N82E168...

or two of the same version but design for only two HD so split them between two PCI slots.

I guess now I will buy the single card only supporting 4 HD on 4 individual channels and get whatever I can from it.

The WD HD I have are not that slow compared to the first revision of SATA that my MB is supporting and they come with 16MB of cache which is not that bad for my system.

Another controller that I am considering is this one: http://www.hardwarereview.net/Reviews/Promise%20FastTra...

Which one do you think would be a better option?

I am leaning more to the 3ware card.

Thanks again for the thoughtful replies.

Nik
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!