The following discussion is not intended to be a pro or con of any vendor, but instead offer a generalized comparison of each products interesting capabilities.
The initial introduction of FAST provides LUN-level migration between tiers, but EMCs upgraded FAST technology will very soon support sub-LUN level migration (1GB chunks of data). The upgraded FAST (due mid year 2010) also includes whats called the FAST Cache, which introduces high-performance flash drives to reduce response times.
The granularity of blocks that are migrated within Compellents architecture are 512KB, but can be tuned to up to 4MB depending upon the particular application.
This includes wide striping of data across SATA drives for the best performance in the capacity tier, and radial placement within the inner and outer tracks of rotating media for optimum performance. Within a tier, 3PAR permits the modification of RAID levels for a given volume for improved protection or performance.
FalconStors NSS also works with their new HyperFS file system, which enables large capacity storage (up to 144PB) and access to billions of files.
The massive growth of archive data clearly identifies the need for storage tiering and the dynamic ability to migrate data between tiers for the best cost and performance benefit. From the vendor discussions, its easy to see that theres a considerable amount of innovation occurring around data migration and other increasingly important storage services as it is, and will be a growing problem in the future.
While automated storage tiers and data migration are becoming checklist items for storage vendors, research continues to identify new optimizations and benefits while seamlessly integrating with other advanced features. You can read about some of this research in resources section at the end of this article.
In the following pages I'll explore some of those services and along the way touch on many of the related evolutions and revolutions that are happening today.
From a 30,000-foot view, automated data migration is about optimal placement of data. This optimization is a joining of the current characteristics of the data to the desired characteristics of the storage medium. For example, placing hot data on high-performing solid-state disks (SSDs) and cold data (or archive data) on cheaper storage such as SATA drives.
What makes this a challenge is that both elements have a tendency to change over time. New data tends to be used more often, but over time as it ages, its used less frequently. Further, storage mediums continue to evolve and diversify, creating new opportunities for storage tiers and matching data to storage characteristics.
Data migration is also useful in the context of advancing storage systems. Data migration provides the transparent ability to migrate data from an aging storage system to a new storage system, even online while users continue to make use of the storage in motion.
Lets begin our discussion of storage tiering and data migration with an introduction to modern storage systems and their fundamental characteristics.
Storage subsystems rely on a number of tricks to improve performance, typically based on caching and striping data, but ultimately their performance is a function of the storage medium. For this discussion, well focus on a few drive examples that have different characteristics to later lead us into the purpose behind storage tiers.