Mass Storage Layout

The Mass Storage System consits of the following hardware:

Two StorageTek Powderhorn tape libraries (9310), each with a 6000 tape cartridge capacity (720 TB with T9940A tapes). The robotics are capable of 350 exchanges per hour.

8 RedWood drives - 50GB cartridges, 10 MB/s, helical scan tape, 17 second tape load and position time.
10 9840 drives - 20 GB cartridges, 10 MB/s, linear format tape (2 reels in cartridge - mid-loading), 4 second tape load and position time.
15 T9940A drives - 60GB cartridges, 10 MB/s, linear format tape, 18 second tape load and position time.

Data Mover Host mss1 - Sun Enterprise E4000 (4 processor, 2 GB RAM, Gigabit Ethernet) with SCSI attached RedWood and T9940A drives.
Data Mover Host mss2 - Sun Enterprise E3000 (4 processor, 2 GB RAM, Gigabit Ethernet) with SCSI attached RedWood and 9840 drives.
Data Mover Hosts mss3-12 - Linux PC (2 processor, 512MB RAM, Gigabit Ethernet) with SCSI attached 9840 and T9940A drives.

The Mass Storage System uses the following software:

JASMine - Controls media access and the transfer of data between tape, stage disks, cache servers, and clients.

Raw data from CLAS is written directly to tape via one or more of the Data Movers. The data is transferred from the CLAS data aquisition system to the Computer Center via gigabit ethernet. The raw data from other experiments is first copied over the network to the staging disks on mss2. Once staged, the files are copied to tape. This allows the system to utilize the tape drives at their maximum IO rates.

Client requests are queued and scheduled. Once a request begins execution, the data files are first written to the staging disks on the Data Movers. Once staged, the files are copied to their final destination. The staging of data to disk allows the system to utilize the tape drives at their maximum IO rates and to free up clients writing data to tape sooner than if they had to wait for tape resources.

This document is maintained by {helpdesk@jlab.org}