Prestage

In the process of [[Upload|uploading files] to tape, they are copied to a tape-backed dCache disk area. From there, they migrate automatically to tape and after that, the least-used will be deleted from the dCache when disk space is needed. Files existing only on tape will be copied to the dCache disk if a user attempts to access the file through its /pnfs filespec or a user starts a SAM job to read the files. It takes up to one minute or more to mount a tape and find a random file. Backlogs at times of high demand on tape drives can cause hours of wait time. Prestaging a dataset is possible and recommended in most cases.