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Is there a performance benifit using a RAID 0 configuration over a PCI Bus

rdilena
rdilena asked
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Last Modified: 2010-04-26
I have recently purchased an HP a1350n AMD 64 x2 with a 250 GB SATA II hard drive.  I am using this machine for my main desktop and am looking for the best performance while using multiple "recourse and data intense" apps and large file read/write operations.  

The motherboard has two slots for SATA cables a PCI e and 3 PCI slots.  The second available SATA slot is for an additional drive for additional storage, there is not onboard RAID controller

I am currently using a multiple monitor setup that uses a gForce PCI e card and only have 1 of the 3 PCI slots available.  I have done some research on PCI cards that provide RAID solutions but have not been able to clearly determine if the read/write speeds would be better running RAID 0 through the PCI bus or just using a single HD connected to the SATA port on the motherboard.  The current HD is large enough for my needs and I would be willing to sacrifice the PCI e graphics card if it meant a "significant" speed gain by using a PCI e RAID controller card.  

Would a SATA II RAID 0 PCI or PCI e card solution (up to about $200 US) provide a significant performance increase?

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Irwin SantosComputer Integration Specialist

Commented:
You need 2 physical hardrives to run RAID 0.  A hardware solution is what you are looking for.  PCI-e preferably.
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Top Expert 2012

Commented:
The PCI bus is significantly slower when accessing hard drives, because the PCI bus is limited to 33MHz and is shared by all devices on the bus.  A connection directly connected to the motherboard will have a theoretical 150MHz limit for SATA1 and 300MHz for SATA2, though in reality it will be less because the hard drives can't deliver data that fast.  I tried a RAID-5 array with 4 SATA2 drives on a PCI slot and I saw only 40MB/sec throughput using HDTach.  A single drive hooked up directly to the motherboard can achieve 70MB/sec sustained.  A PCI-e connection would be better and could probably maintain the maximum throughput that the drives are capable of.

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Commented:
Callandor... Excellent thank you.  sounds like i should stay with my onboard connection or maybe the PCI e option.  Any Idea about the kind of speed gain (if any) possible using raid 0 on a pci e card and bus.
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Top Expert 2012

Commented:
Using 2 WD Raptors in a RAID-0 array, I was able to achieve 100MB/sec sustained transfer rates connected to an MSI K8N Neo2 motherboard.  I had 2 7200rpm drives in a RAID-0 setup on another machine connected to the motherboard and got about 90MB/sec sustained.  I haven't tried PCI-e cards yet.
Irwin SantosComputer Integration Specialist

Commented:
If you are utilizing the RAID for data, then you better off with a separate drive for your OS, and in your array 2 drives. That is a total of 3 drives. When you are searching for data, it won't be impeded by the OS.
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Commented:
Well ... it's not quite so simple.

First of all, SATA 150 and SATA 300 are NOT 150MHz and 300MHz clocks -- they're actually much faster than that ==> the 150/300 refers to the transfer rate in MB/s (the clock is more like 1.5GHz to clock all of the bits plus parity to achieve the 150MB/s transfer rate.).

Second, the 33MHz PCI bus frequency results in data transfer rates about 132MB/sec, since the bus is 32-bits wide.   In fact, on server motherboards that have either 64-bit PCI slots or 66MHz PCI slots the transfer rate is double this; and on boards with 66MHz 64-bit PCI slots the rate is quadruple that !!
(of course most systems don't use server motherboards)   Further, the overhead is very low if you're using a bus-mastering PCI RAID card -- since it takes over the PCI bus during its transfers.

That's why the better RAID cards can achieve very nice transfer rates -- well over 100MB/s sustained rates.  Granted, a 33MHz 32-bit PCI slot is still limited to 132MB/s -- but that's a lot better than what was implied above.

For MOST systems -- that aren't using the PCI bus extensively for other things -- a PCI RAID card will give very nice performance.    Clearly if you have a PCI-x slot available you can get even better performance; but remember that 132MB/s is an outstanding SUSTAINED rate.   Unless you have more than 2 drives in a RAID-0 array, that's probably about as fast as you're going to achieve with ANY controller.   I think you'd be very satisfied with a good (e.g. 3ware) PCI controller and a nice pair of high-performance drives (e.g. Raptors).

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Top Expert 2012

Commented:
Oops - Gary is right, my feeble mind was comparing SATA's 150MB/sec transfer rate with the ATA133 spec, which is basically apples and oranges.  However, my data was obtained from a HighPoint 1820A PCI-X card, which isn't in the same league as 3Ware cards, but does fit the $200 limit.  If you go with 3Ware, be prepared to spend $300 and up, perhaps $500.
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