In
the far northwest corner of the computer room is an integral part of the
Mass Storage System (MSS). Impressive in dimension, these five StorageTek
Library Storage Module's (LSM) stand almost 10 feet high and
contain thousands (5389 each) of data cartridges. When a program is submitted
that calls for data stored on one of the cartridges, the LSM device will
retrieve the appropriate cartridge and place it in a drive.
Each LSM has a robotic arm with two mechanical hands
mounted on a post. The post sweeps around the center inside the LSM while the
two attached arms move up and down the post to access cartridges. To find the
correct cartridge, the arm is equipped with a laser eye that scans the barcode
number on each cartridge. The mechanical hand will grasp a requested
cartridge and mount it in an available cartridge drive.
In one LSM are the STK 9840 cartridge drives using 9840
type cartridges.
Each cartridge has two reels inside. The tape is wound around both
reels providing a mid-point load. The cartridge then moves one way or the other as it accesses the data needed. Each cartridge holds 20 GB of data, and
data can be transferred at a rate of 10-11 Mbytes per second. 10 drives only
use an area 6 feet by 2 feet 5 inches when they are stacked one on top of the
other. Approximately 120 Terabytes of data will be stored in each LSM on the
9840 cartridges. In another LSM are the STK 9940 cartridge drives. STK has
returned to the older single reel construction which allows these cartridges to store 60GB of data each.
Photo courtesy of Lynda Lester/SCD
To see construction of an LSM from the ground up, see the
virtual tour here.
Across the room to the south is the IBM 9672. It is the Mass Storage Control Processor (MSCP) of the mass storage system. By providing access to disks and cartridges, it allows the various computers to read and write data. While disks store small files, cartridges store larger files. When the data has aged off of the disks and LSM cartridges, it is moved to the archival cartridges.
The 9672 keeps track of where the data is in the same manner that a library keeps track of a book. It has a label for each piece of data and it has a directory of where that data is stored. The directory is called the Master File Directory (MFD). Because data is always moving from one storage medium to the next, the MFD is updated every day.
The data stored and managed by the 9672 represents computed and observational data gathered throughout the years here at NCAR and around the world. As of Fall 2003, over 1.5 petabytes of data are stored on the Mass
Storage System. Visit the SCD site for additional information about the
Mass Store.
