Fast guide to fancy SAN management

No longer tied to a monolithic enterprise price tag, many of the sophisticated storage management capabilities outlined below can now be found in affordable SAN midrange systems from Compellent, iQstor, Xiotech, and other vendors.

Automated data migration allows data to be moved from expensive first- or second-tier storage to cheap SATA-based storage, without manual intervention by the administrator. Automated data migration helps ensure that the highest-performance storage is reserved for the most active or most valuable data.

Automatic volume expansion allows for a thin-provisioned volume to grow automatically when it reaches a threshold. If the volume reaches, say, 80 percent of capacity, then additional capacity -- as long as it's still available on the system -- could be provided automatically.

Boot from SAN allows for servers to boot from the SAN rather than internal disk. This, combined with snapshots and mirrors, allows for one server configuration to be copied and used for a number of physical servers. Since the copies can be made very quickly, a single configuration can be used to boot hundreds of servers in a very short period of time. Combined with automated management tools and server virtualization software, boot from SAN allows administrators to have a pool of server hardware that can very quickly boot any of a variety of operating systems and server software to meet changing requirements.

Content addressed storage (CAS) provides a way for data to be archived and retained for a set period of time without being changed. Data is stored using a hash algorithm that verifies data integrity and proves that data hasn’t been modified since it was stored. CAS is used primarily for meeting requirements for legal discovery and archiving requirements of standards such as Sarbanes-Oxley. CAS is not (yet) available on any of the midtier systems I have tested.

Continuous data protection (CDP) is a journaled synchronization process, usually asynchronous, that allows more control than simple replication. Because each change to each item that is replicated is added to the journal, it is possible to find and restore a specific version of any file that has been changed multiple times, providing a degree of granularity not available with replication alone.

iSCSI support allows the system to provide storage via either the FC (Fibre Channel) interface or an Ethernet interface. Systems that support remote replication can also easily support iSCSI, since both use (and require) an Ethernet interface and TCP/IP capability. The Compellent, iQstor, and Xiotech SANs I tested all support iSCSI. The Xiotech and Compellent systems included the hardware and software necessary, while the iQstor system included the software but not the required hardware module.

Mirroring is another name for local replication. Mirrors can be created, and then broken, so that two initially identical volumes can then be used for different purposes.