By Steve Duplessie
For years, a simple concept has plagued end users and systems integrators who have valiantly tried to implement storage area network (SAN) technology: How do I keep one system from stomping all over the file system of another? Secure access control has been a major nemesis for SAN adopters.
SAN technology was touted as an answer to all IT storage problems. SANs
enable IT administrators to connect lots of heterogeneous servers over a high-speed wire to centralized, shared storage pools. However, what we got was a high-speed wire, and an enormous headache. Instead of being the end-all, early SAN implementations often resulted in less secure environments.
SAN appliances virtualize storage resurces into a pool, or storage domain.
Being able to partition SAN elements logically has been a long-time goal, and one that has been addressed in many ways to date. Finally, however, we have some light at the end of the tunnel: the SAN appliance.
Here's what IT managers need:
- The ability to create Logical Unit Numbers (LUNs) from a shared storage pool, regardless of what type of storage it is. Users typically have storage subsystems from a variety of vendors, and would like to use all of them in a SAN environment. They will not tolerate vendor "lock-in."
- The ability to allocate individual LUNs to one or more servers on the SAN.
- The ability to create "snapshots" and multiple mirror copies outside of the disk arrays and hosts. This should be a standard procedure, regardless of manufacturer.
- The ability to perform other tasks, such as remote mirroring or bridging to IP, from a single platform regardless of which other vendors are on the SAN.
Switch vendors provide zoning, but zoning is typically an all-or-nothing proposition because you can't zone down to the LUN level, which sort of defeats the point of a centralized storage pool.
Disk array vendors have done their part in making SANs usable, but they often pursue a "lock-in" strategy that limits you to a particular vendor's hardware and software.
Another partial solution is host-based volume managers, but because there are so many iterations, this approach often doesn't work well in a mixed platform environment.
Enter the SAN appliance, which provides the ability to perform all-or most of-the necessary functions from a single box. Think of it as universal volume management outside of the host. I love this concept. These boxes sit between the hosts and the storage and allow administrators to "virtualize" all of the disks, and to carve up the storage pool any way they want.
SAN appliance vendors currently include Compaq, DataCore Software, DataDirect Networks, StoreAge, StorageApps, True-SAN, and Veritas Software. DataCore and Veritas provide software-only solutions, while the other vendors are predominantly hardware based.
However, you'll start to see a barrage of SAN appliance offerings over the next few months. Some appliances will sit in the data path, some will reside out of the data path (there's always something to argue about). And some will be implemented in host software, while other appliances will be primarily standalone hardware devices. They all share one thing in common: They perform volume management outside of the hosts, and that's a good thing.
With the advent of SAN appliances, we'll start to approach the levels of SAN utopia that we all hoped for.
Steve Duplessie is an analyst with The Enterprise Storage Group, a storage research and consulting firm: www.enterprisestoragegroup.com. He can be reached at firstname.lastname@example.org.
Steve Duplessie, The Enterprise Storage Group