A 3-Tier RAID Storage System with RAID1, RAID5, and Compressed RAID5 for Linux

This paper presents the design and implementation of a host-based driver (a ``volume manager'') for a 3-tier RAID storage system, currently with 3 tiers: a small RAID1 tier and larger RAID5 and compressed RAID5 (cRAID5) tiers. Based on access patterns (``temperature''), the driver automatically migrates frequently accessed data to RAID1 while demoting not so frequently accessed data to RAID5/cRAID5. The prototype system, called ``Temperature Sensitive Storage'' (TSS), provides reliable persistence semantics for data migration between the tiers using ordered updates or logging. Mechanisms are separated from policies through an API so that any desired policy can be implemented in trusted user processes. We also discuss the problems faced while moving from the original implementation on the Solaris platform to Linux. Finally, we present comparison of the performance of our design with comparable systems using striping or RAID5.