Help with RAID 5 setup

I am thinking about making a Linux box with it's main function being a file server used for backup. In the future I may also give it other responsibilities such as a webserver, but for now what I mainly want it for is for backup. I was thinking about using RAID 5 since wastes only 1 HDD of space (25% in my case) while still providing redundancy.

Right now I have a Socket A Sempron 2200+ on a Biostar Mobo with only PCI slots with 512 MB of RAM. I also have a Socket 939 Athlon 64 3000+ lying around, but no Mobo for it.

It looks like my choices are (in order from cheepest to most expensive):

1. Buy a Mobo such as this one that has RAID 5 built in and use the faster Athlon processor.

2. Use the Sempron and Mobo I have now and buy a RAID 5 controller. Due to the limitations of the Mobo, my only choice is a PCI controller and I am afraid that I will regret not getting a faster PCI-Express one later if I ever want to upgrade.

3. Buy any Socket 939 Mobo w/ PCI Express and purchase a faster PCI Express RAID card.

4. Purchase this and a PCI Express RAID card. This option is kind of random, but since the processor is a mobile one I figured it would use a lot less power and might be smarter to use for a PC left on 24/7.


I plan on use 4 HDD with this array. I have never worked with any type of RAID other than software RAID 0 done with Win XP. My biggest priority is that my data is safe and I do not have to worry losing my data due to hardware failure. After reliability my priorities are price, and then finally performance.

Any suggestions or comments would be nice.


If I chose to purchase a dedicated RAID controller I was thinking about either this or this. Both are HighPoint RocketRAID 4 port SATA models. The first is a PCI version and the second is a PCI Express 1x. Any comments on these controllers or any others would be nice too.

Here are a few things that you should keep in mind:

1. One modern SATA HDD can push through 50 MB/sec at the low end for 7200 rpm 40GB drives on up to nearly 90 MB/sec for the Raptor 150. I assume that you're somewhere in the 250-400 GB range, so figure 60-70 MB/sec as maximum throughput from the HDD.

2. RAID 5 can have read speeds almost near RAID 0 levels, so it's entirely possible to have a read speed of four times the maximum speed of one HDD, so figure 240-280 MB/sec as maximum drive throughput.

3. Normal 32-bit, 33 MHz PCI busses have a shared total bandwidth of 133 MB/sec. So only consider using a PCI SATA controller if you're using one or two drives. More than that and you'll not have nearly as good of performance as you are capable of getting due to bus saturation. Also realize that a lot of PCI bus traffic will require a lot of CPU utilization.

4. A single-lane PCI Express card such as the HighPoint 2300 has 250 MB/sec throughput in each direction. So if you buy a PCIe x1 card, know that you're bus-limited to 3 fast drives or 4 normal ones.

5. There are PCIe SATA cards that have x4 or x8 interfaces that won't get bus-limited with a dozen HDDs, let alone only four as four lanes gives 1GB/sec and 8 lanes gives 2GB/sec throughput. HighPoint's 2310 is otherwise exactly identical to the 2300 you noted but it's PCIe x4.

6. Motherboard-based RAID as well as the HighPoint units simply use software "fake" RAID. You're better off just letting the drives show up as disks in Linux and using md to configure a software RAID. md is much more flexible than any other fake-RAID or hardware RAID implementation and it's at least as fast as fake-RAID or even a good hardware RAID controller like the expensive 3Ware 9650 series.

7. Note that on some motherboards, particularly NForce ones, that running RAID from the onboard ports can be slow. See THG's NForce 680i vs Intel ICH7R (975X) vs Intel ICH8 (965) that they posted today for more info. I am running a RAID 5 using md on a NForce 4 board and it's giving me about the same seem-to-be-bus-limited performance as the 680i gave Tom.

I suggest that you get a 939 SLi or CrossFire board so that you can put the Athlon 64 3000+ in and get a high-bandwidth slot to put a PCIe x4 or better SATA card in, if you are so inclined. Those boards shouldn't be more than $100 anymore- I got my abit KN8-SLi for $115 in February and they've dropped in price a bit since then.

I actually ordered the HighPoint 2310 so I can add another drive as I ran out of motherboard SATA ports. It should be arriving within a week, so I'll put attach the HDDs to the 2310's ports and see if md likes that better. The Linux driver does compile okay on a new 2.6.19 kernel, in case you wonder. I'll help you through it if you need it, but HighPoint's documentation seems to be pretty good.