We purchased a dell poweredge 2800. it came with 4 drives with RAID controller. i installed Server2003 using dell management software. now it it made the RAID 5 using all 4 drives. is ther anyway that i can have 1 drive for OS (seperate) and the rest 3 for RAID 5 ? what are the disadvantages or advantages for this confuguration ? and what would you guys suggest. im new on server side.. looking forward for your help

Presently with all 4 disks in a RAID 5 array you have redundancy. If one drive should fail, it's not a big problem, you replace the defunct drive and the RAID rebuilds and life goes on as before without any downtime or loss of access to the data on the server. However, if you change to a single disk for the OS and the other 3 in a RAID 5 configuration, what happens to you if your single OS disk becomes bad? I'll tell you, your server shuts down and all the data on your server is no longer accessible until you buy a new disk, replace the old one, reinstall your OS, recreate your domain and then reinstall all your backups. That's an awful lot of downtime with your server unusable and the data on it unaccssible. Your best bet is to leave things as they are. That or buy another hard drive and use two to create a RAID 1 for the OS and use the other 3 for data in a RAID 5 configuration.

Couple of considerations. You should have set the 4th drive as a hot spare so if any of the 3 drives failed you would have had instant failover. Raid5 is not recommended for maximum pagefile operations. A OS and Data partition on raid 5 means you can not upgrade the disk space on the OS partition without a complete reinstall. If you don't partition and have a single partition for the entire drive you also will not be able to add any additional space in the future to the Os drive unless you have a smart controller that can dynamically add additional drive space to the array. You would get better performance imo from having two raid1 arrays [mirrors] with OS on one and data on the other. It has been tradition to mirror the OS and raid 5/10/0+1 the data. This makes it easy to expand the data array. Backup, add the disk(s), reinit the array and restore from backup. I have done it on a single sat and it was a short day. I consider performance wise raid 5 to be the worst. But it provides fault tolerance which is better than standalone drives.