SSDs don't always provide best performance. They read the data in ordered blocks, which may not be what the database needs.
When deciding what RAID and filesystem to use for a database, the important questions are:
- How large is the dataset / drive?
- How much money do you have?
- Is it read-heavy or write-heavy?
If the dataset is large, i.e. > 10 TB, you will want avoid RAID5. You could lose a second drive while rebuilding the array, resulting in a total loss of data. RAID6 and RAID10 are good profiles, but be aware of the restrictions with RAID10. Also: Pick a journaled filesystem that doesn't require a regular fsck-ing; in other words, avoid ext3 and go with something like xfs... or better yet, go Solaris and use zfs. Do you have any idea how long it takes to fsck a 10tb volume?
If you have more money, you can buy an external cabinet and might get some additional speed boosts since the machine won't be trying to do system activity (logging, etc.) while reading from the dataset. You can also get a better RAID controller with more RAM and higher throughput, or faster disks. Basically, you get what you pay for.
If the data is read-heavy, you can stick to Raid10. If your data is balanced read/write or write-heavy, you'd probably better stick with raid6.