U.S. Geological Survey National Mapping DivisionEROS Data Center Digital Archive Media Trade Study 8/27/01 By Tom Bodoh Archive Media Study Project Manager

U.S. Geological Survey National Mapping Division Outline  Purpose Of The Study  Technical Approach  Background  Evaluation Criteria  Findings  Conclusions  Recommendations  Further Thoughts

U.S. Geological Survey National Mapping Division Purpose of The Study The purpose of the study was to analyze long-term offline digital storage technologies and recommend which technology should become the next EDC archive media of choice and be deployed for the Landsat Archive Conversion Study (LACS) project.

U.S. Geological Survey National Mapping Division Technical Approach  Study focused on four drives  Quantum SuperDLT  Seagate LTO Ultrium  StorageTek 9940A  StorageTek 9940B.  All drives would be benchmarked (9940B not available for benchmark until October).  Drives would be rated on reliability, performance, and cost.

U.S. Geological Survey National Mapping Division Background  The goal of the LACS project is to convert Landsat 1-5 Archives to fully digital media, reducing space requirements by more than 80% and future transcription costs to less than $100,000.  LACS will produce two copies, a master and a working copy.  Future transcription will involve simple tape copies which would be automated with scripts and silos, and would complete in weeks or months instead of years or decades (or even perpetually).  Use of digital technology will facilitate a transition to robotic archives.

U.S. Geological Survey National Mapping Division Background Technologies used for current EDC archives;

U.S. Geological Survey National Mapping Division Evaluation Criteria Criteria in decreasing order of importance: 1.The primary criteria for selecting a digital archive media is reliability. A second copy will reduce risk somewhat, but a reliable technology is mandatory. Reliability is proven over time. 2.The secondary criteria is performance. The capacity must be high enough to save significant space and the transfer rate must be high enough to allow transcription to occur in a timely manner. 3.The tertiary criteria is cost. The actual drive cost is fairly insignificant, but the media cost is quite important.

U.S. Geological Survey National Mapping Division Findings: Reliability SuperDLT reliability: 1.SuperDLT is similar in design to DLT 7000 which has proven problematic. When DLT 7000 errors occur, a higher percentage of data is lost as compared to 3480/3490 since data cannot usually be recovered past the error and the error typically occurs repeatedly. 2.SuperDLT utilizes 56 serpentine passes, causing concern of tape and head wear. 3.SuperDLT is targeted to the write-many/read-rarely backup market where errors are expected on write and recovery entails a simple rewrite.

U.S. Geological Survey National Mapping Division Findings: Reliability LTO reliability: 1.The first tape tested experienced an unrecoverable media error on read. Data could not be recovered past the error, similar to DLT LTO utilizes 48 serpentine passes, causing concern of tape and head wear. 3.LTO is targeted to the write-many/read-rarely backup market where errors are expected on write and recovery entails a simple rewrite.

U.S. Geological Survey National Mapping Division Findings: Reliability 9940A reliability: A is similar in design to the 3480/3490 and is based on the proven EDC has experienced almost no data loss with 3480/3490. ECS has had good (though brief) experience with The 9840 has performed well at EDC for the past 18 months A utilizes 18 serpentine passes, causing less concern of tape and head wear. Additionally, nothing touches the recording surface A is targeted to the write-once/read-many archive market where errors are expected on read and recovery entails stringent ECC or recovery from a master copy.

U.S. Geological Survey National Mapping Division Findings: Reliability 9940B reliability: B is a follow-on product to the 9940A, therefore a descendant of 3480, 3490, 9840, and 9940A. All of these drives have proven reliable at EDC. 2.Since the 9940B drive does not ship until June of 2002, reliability can only be projected based on past experience with StorageTek and their products B will utilize at least 18 serpentine passes and nothing touches the recording surface B is targeted to the write-once/read-many archive market where errors are expected on read and recovery entails stringent ECC or recovery from a master copy.

U.S. Geological Survey National Mapping Division Findings: Performance Capacities and transfer rates: (Note that all results are without compression)

U.S. Geological Survey National Mapping Division Findings: Cost Cost of four drives, and 320 TB (two copies) of media: (note that 9940B price is for Fiber-channel model)

U.S. Geological Survey National Mapping Division Conclusions Weighted decision matrix:

U.S. Geological Survey National Mapping Division Conclusions  Although SuperDLT and LTO have projected an upgrade path, 9940B should be the performance and cost leader for months after it ships.  SuperDLT typically does not come close to their rated capacity (89%) and transfer rate (57%).  SuperDLT loses a greater percentage of data when errors occur – as compared to 3480 and  LTO experienced unrecoverable data loss on the first tape tested at EDC.  All four drives use serpentine recording but 9940A/B minimizes it and does not touch the recording surface.

U.S. Geological Survey National Mapping Division Conclusions  While all drives are compatible with robotics, only the 9940A/B are compatible with our large existing silos.  9940B is the clear performance leader.  SuperDLT and LTO are targeted to the write- many/read-rarely backup market, while 9940A/B are targeted to the write-once/read-many archive market.  An alpha 9940B drive will be demonstrated in early October, and a beta drive will be available in February.  Though the 9940B will not ship until June of 2002, there are compelling technical and cost reasons to wait for the 9940B.

U.S. Geological Survey National Mapping Division Recommendations It is recommended that the StorageTek 9940B drive be designated as the next EDC digital archive media of choice, and utilized for LACS. Orders for the 9940B may be placed in the February timeframe. The LACS configuration calls for four drives on three systems (two for LACS transcription, one for LACS validation, and one for NLAPS ingest). Since only two drives are budgeted in FY02 it is recommended that the drives be shared via Fiber- channel in order to provide flexibility in the case of changing requirements or drive failure.

U.S. Geological Survey National Mapping Division Further Thoughts  The 9940C is scheduled to ship in 2003 and is slated to have 500 GB capacity, 40+ MB/sec transfer rate, and a media cost of $160/TB.  With 200 GB 9940B cartridges, one 160 TB copy of the archive would fit on 800 tapes, and only 320 tapes with 500 GB 9940C cartridges. Robotic access to the working archive becomes feasible.  A silo could automate future transcriptions.  Although LTO and SuperDLT are unsuitable for critical archive use, they should not be dismissed for data interchange, backup, or other less critical storage.