Storage Hardware
Our primary networked storage device is our Storage Area Network, or SAN disk array. We have a StorageWorks EVA 6000, made by HP. The third array we've used, it is located in the Learning Center in the area housing the telephone switch we use for the front of campus. In June of 2007, it replaced our EVA 3000.
Our EVA 6000 has about 5 terabytes (roughtly 5000 gigabytes) of storage space available, and we're using about 75% of it at this time. HP recommends 90% usage as the upper limit; after that, performance degrades. The EVA 6000 contains 20 highly reliable 300-gigabyte fibre-attached drives. At this point, we estimate adding storage would cost in the neighborhood of $15 a gigabyte. That seems a lot compared to PC drives, until you realize that these are high-performance drives. The industry uses mean time between failures as an estimate of hard drive reliability. Our SAN drives are rated at 1.5 million hours MTBF at a constant activity level. A standard consumer PC drive is generally rated for 500,000 hours MTBF at 20% usage.
The two controllers that run the EVA 6000 can take over for each other. A single controller failure will not interrupt service. Nor will failure of a single power module or a single fibre channel switch.
The GroupWise Email servers are split between Learning Center and Brothers College, as are the Netware servers we use for file and print services (Causeway). All are dual-connected, so a single fiber optic cable or fibre channel switch failure cannot interrupt service.
One database cluster server, which also runs our backup software (the second cluster server is in the Learning Center) and our backup devices are located in Brothers College. This ability to locate our backup system in a different building than the storage array itself was a major factor in our investment in SAN technology three years ago. We are using fiber optic cable between the buildings to link the BC hardware to the SAN. The only drawback is the distance; with our current hardware, it has been difficult to maintain a 2GB fibre channel link between the buildings.
Backup Hardware and Software
We are using Syncsort Backup Express as our Enterprise backup solution. It provides excellent support for Netware, Linux and Windows, our three primary server operating systems, in addition to major commercial Unix variants like HPUX and Solaris. This was a significant investment we made during the course of the 2003-2004 academic year when increasing storage demands made it necessary.
Our 87-tape autoloader library in Brothers College has a storage router attached to it that allows it to be attached to the SAN. Some of our servers can directly access the tape drives without having to pass all of the data over our regular network links. The tape library is actually two linked HP StorageWorks MSL6000 libraries, a MSL6030 one holding 29 cartridges and two LTO-3 tape drives. The other unit is an MSL6060 with no drives, but 58 slots for tapes. The base capacity is 400 gigabyte per tape. With optimal compression (rarely achieved) you can get as much as 800 gigabytes on a tape.
In an attempt to address some of the performance and capacity limits of our tape hardware, we have aquired a second, lower-cost fibre channel-attached disk array, an HP Storageworks MSA1500cs. It uses lower-cost, high-capacity SATA drives. These drives do not perform well enough to replace the production SAN hardware for day to day use, but they have proven adequate for performing "backup to disk," where the backup server acts as if it is communicating with a tape device, but it is really creating a file on a disk. This is faster and more flexible than our current tape storage. It does not provide the ability to archive or store tape media in another location, though, so it is not a complete replacement for tape backups.
Server-Based Storage
Some servers (notably the servers used by Computer Science and some of our VMware ESX virtual server hosts) rely on local storage. For various reasons, it made sense to do that in these specific cases to avoid the up-front cost of attaching them to the SAN. Our general policy is that any critical server with end-user data relying on local storage has to be located in the Learning Center or Pepin. That way, it is not in the same physical location as our backup system. Servers relying on SAN-based storage can be located in either facility.