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- Shared Resources: Tape drives are shared among all users. If multiple users request data from the same tape simultaneously, retrieval times can increase due to the queue that forms.
- High Demand Periods: During peak usage times, the competition for tape access intensifies, leading to longer wait times.
- Archive Catalogue Data OrganisationRetrieval Overview: When reaching the final step of the Archive Catalogue (accessible at ECMWF Archive Catalogue), where data retrieval or request visualisation is possible, all the displayed information corresponds to a single tape file.
- Exception for Stream ENFO (Since IFS Cycle 48r1, 2023): With the introduction of Cycle 48r1 in 2023 and the increase of ensemble forecast resolution, the single forecast data within the stream enfo is split across three tape files. This split is based on the time step and happens in the parallelisation during the writing process. As a result, these three tape files are often located on separate physical tapes.
- General Rule: Outside of the enfo scenario, a single forecast is always stored on one tape file, which is guaranteed to reside on a single physical tape. While in most cases multiple tape files reside on one tape, there isn't an exact order with which these files are written. : Each forecast cycle is stored in a separate tape file. Requesting data over a long time range—such as a month's worth of ensemble forecasts made twice daily—means accessing numerous tapes. Since MARS stores data by date rather than by parameter, certain requests can be less efficient and slower to process.
Even if alternative methods were used to provide the data, the underlying issue remains: the data must still be retrieved from the same tape system, and the limitations apply universally to all users.
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