Running SSD’s in RAID can get very expensive very quickly.  A more cost effective solution is to have a disk RAID and use an SSD as a cache.  I’m not sure if any of these are production ready but all are worth watching:

• zfs-fuse - supports the ZFS L2ARC feature which can be used to setup an SSD as a cache for a ZFS pool.  Checksums SSD data and supports multiple devices.
  • ZIL and L2ARC cache questions
  • ZFS – zpool ARC cache plus L2ARC benchmarking
  • How stable is zfs-fuse 0.6.9 on Linux?
• bcache - a recent project for caching linux block devices. Currently only supports 1 cache device and offers no checksumming.
  • Bcache: Caching beyond just RAM
  • Want to use an SSD as cache? Now you can
• flashcache - created and released by and for facebook this at least seems to be in production. documentation is not great however.
• Facebook releases Flashcache

Abandoned Projects: