IMHO, the Intel Dual Xeon 3.2 GHz with 4 GB RAM and
(4) 250GB SATA RAID 0+1 - 500GB Usable Hard Drives maybe more usefull for you if you use it for hosting.
The strength of RAID 0+1 is it's data throughput and I/O transfer rate. It combines RAID 0 (stripping which is fast) and RAID 1 (for redundancy). Plus the size ... 500GB is a lot.
In terms of usability, with 500GB usable data, you can do a lot of things with it. In terms of performance, SCSI may out perform SATA in some cases but SATA should be fast enough for almost all web applications, specially when it is RAID 0+1. For redundancy, RAID 5 and RAID 0+1 is about the same.
For hosting, I believe the SATA has slight advantage over the SCSI in terms of business perspective and functionality. But performance wise, SCSI should be a little faster.
I have a Dell PE 1800 and PE 2850 with samiliar configuration except the HD. The 1800 has CERC with RAID-0 SATA (7200.8 with NCQ). The 2850 has PERC with RAID-1 15k SCSI.
Passmark shows very similar performance on everything except the HD - the 1800 scored 250, the 2850 scored 350, despite 1800 has RAID-0 and 2850 had RAID-1.
I think RAID-1 and RAID-5's performance would be close. 10k SCSI drives would have brought the score down to around 240. Using SATA drives without NCQ will reduce the performance somewhat too. With everything considered, I think the RAID-0+1 SATA would score about the same as RAID-5 SCSI or a little lower.
However (a big however), like KarlZimmer said, the choice of RAID card is important. If the SATA RAID card depend on the CPU for processing, it will reduce the speed (and reliability) significantly. If it is a quality card (like 3ware), it will be fine.
As a note. I also recommended the SCSI setup as I don't see any use for 500GB on one system in a typical web hosting setup. We have a decent sized shared hosting customer base and we use high end dual Xeon systems with RAID arrays, etc. on all our systems and none of them are using over 100GB of disk space... If you go with 500GB and don't overload the system you're likely looking at a lot of wasted disk space, though of course everyone's situation is different.
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Does raid 0+1 offer the same level of security has raid 1? If one hard drive goes bad, will my data and server still be fine?
In terms of security, yes. However, raid 0+1 will boost the performance as well. For hosting business, SATA with raid 0+1 is good, just make sure you get good controller card. If you are only looking for servers, there is one recommondation. jhpcomputer.com/catalog
Raid 10 or 1+0 is better than 0+1 in the case a drive goes bad. With RAID 10, the one drive is mirrored and you're back to full protection.
With RAID 0+1, your stripe is broken, and the whole stripe has be be remirrored after replacement.
That being said, if the RAID card doesn't do RAID 10, or RAID 1, just RAID 0, then doing RAID 1 in software with the hardware RAID 0 volumes gives you better performance than doing everything in software.
At my work, they did a RAID 0+1 with 11 drives in the stripes, and were shocked when it took 7 hours to remirror the volume using Veritas.