As long as you multiplex your files, you can use them on unprotected devices. If you don't multiplex, I would rather have them on a RAID 5 than an unprotected RAID 0.
I recommend that you use RAID 5 only if you run DSS, a read only Orcale DB (or a system which reads data most of the time).
I use RAID 1+0. It is faster than RAID 5 bacause it has less computation overhead.
Now, you may ask what is the problem with writing in RAID 5. As you probably know fisrt data stripe is read from the array, next the new data is added to the stripe, next you have to compute the new parity block (there are several algorithms for that) and eventually the data is written to the disk.
What I have heard is that after all RAID 5 might decrease writing by 20-30% but it might increase reading (big reads).
I agree with Julian also, I was working on a system with a high insert load, around 700 row inserts per second 24x7, the server was originally set up with RAID 5, but because of the Parity building/checking, it was killing performance. I ended up going straight RAID 0 stripping over 6 drives for the fastest speed. I was running two servers in parallel for failover, therefore morroring and parity wasn't required.
Maybe RAID 0 + 1 (Stripping + Mirroring) would be a good option if you can afford the storage space.
OCP 8i, 9i DBA
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