Simon Seagrave (http://www.techhead.co.uk/) asked, “How long do you think it’ll be before SSD will overtake SCSI as primary tier 1 SAN storage? Giving a new SSD and SATA tiered mix.”

Short answer: Yes, it will be SSDs + SAS and within 2 years.

The real quesion is when 15K RPM highspeed drives will be replaced with SSDs and 7.2K RPM high capacity drives.   SAS will probably end up replacing both FC and SATA in the majority of mid-range storage but the jury is still out on if this will happen in high-end arrays.

What are we talking about here? From an array design perspective, frequently accessed blocks of data should be served from ram and SSD.   SSDs have a much faster response time (microseconds vs. milliseconds) than traditional hard disk drives which enable this possibility.   The Sun Unified Storage platform was one of the first platforms to do this all in one array with their Hybrid Storage Pool design.   There are also some new appliances coming out like the Xcelasan from Dataram.   NetApp offers read accelerationt through their PAM 1 (Performance Acceleration Modules).   EMC will also start the transition at the LUN level with their implementation of FAST as described by Devang Panchigar.   This list is not meant to be comprehensive as I’m sure I have left out vendors and their roadmaps.

When will this happen? I expect the majority of storage vendors to implement this type of solution at the block level within the next 2 years based on current development cycles from most major storage vendors.   It will take some longer than others because of their architectures. It will be a key differentiating feature between vendors.   Beyond basic tiering between SSDs and high capacity disks we should see more advanced algorithms on what data and where to move it to.   I’ve followed journey of Sun’s ZFS   on the zfs-discuss mailing lists over the last year and have noticed that peculiar performance behaviors happen (write-pulsing) have required fine-tuning.