I am planning to set up a RAID array for scratch space use in a computational server (16 cores, 128 GB RAM). The users will routinely be creating large (500GB) MySQL InnoDB databases and storing these temporarily to the scratch space. The databases are filled with data from a cluster which may have up to 1000 MySQL clients connected with a database at once. The RAID controller is a PERC H710 integrated controller with a 512MB non-volatile cache.
Since the storage is temporary, I am planning to use RAID 0 for read/write performance. The remaining question is then whether to use 8 x 7,200 RPM disks or 4 x 15,000 RPM disks. One typical use-pattern will be that once a database is created, there will be very few writes to it. There will be a lot of reads for analysis so the 15K seek time would help here however I do not know how the RPM improvement stacks up against from the RAID 0 striping speed up with extra disks.
Ignoring drive capacity as a factor, which setup would be preferable, 8 x 7200 RPM drives or 4 x 15000 RPM drives? I apologize if this type of question does not have a clear answer.
Edit: I have not looked into how much the RAID controller will limit the effective throughput based on the number of disks in the array yet.