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Archiving

The Computing for Science (CS) group supports ILL scientists, students and visitors in a number of activities including data analysis, instrument simulation and sample simulation.

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Archiving and safeguarding files

R. Ghosh, January 2001

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Safeguarding files - Backups

At regular intervals copies of either all files, or recently modified files are made automatically on cassette tapes. In the case of a disk problem the combination of the full copy plus the more recently modified files allows reconstruction on a replacement disk.

In general the recorded tapes are re-used after a period of some months. Hence if a file is deleted intentionally, after a certain period, there will no longer be any trace of it.

Most workstations are backed-up automatically. This activity is performed by the SI. If files have been deleted accidentally then a call to the HelpDesk (extension 7013) can usually lead to rapid recovery of the most recently saved version. On request the SI will also arrange for backups to be made of PC and Macintosh systems.

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Private Archives on CDs

There are a number of CDrom writers at ILL attached to Group PCs and Macintoshes. These provide a good means for saving up to 650Mb of files in a reliable fashion. Normally files are saved in the ISO9660 standard format, which enables them to be reread on most machines, though inevitably text files retain the line-ending characteristics of the source system (Unix=LF, PC=CRLF, MAC=CR), and binary files may only be read with their original programs. In general the common data compression routines and file archiving routines usually recognize files produced by others. Thus files from Unix tar and zip are recognized by Mac-Stuffit/Expander and PC-WinZip.

 

Retaining Creation Dates
Normally transfer using ftp results in the copy being given the current date. Similarly, with Unix systems, the cp command gives a new date to the copy, unless the -p switch is deliberately added. Moving a set of programs using tar, or by compression-archive utilities like zip allows the file to be restored with its original date. The utilities gzip and gunzip only compress or decompress single files, and must be used in conjunction with tar. The unix tar files include the full unix characteristics, whereas zip files have no notions of user identifiers.

 

NOTE: tar and zip files must be transferred using ftp in BINARY mode

Thus data can be easily packed together on a Unix system before being transferred by ftp or other means (e.g. using SAMBA file-sharing between serhom and PCs). The zip file can then be written as it is onto the CDrom, or uncompressed locally and separate files written. In general the software, eg Adaptec Toast (MAC) or Adaptec CD Creator will accept most filenames. If there is doubt then the compressed file can be saved, with its internal names.