FAQ

What changes are needed  to a jsub script when the job stages files to the write-through cache system?
There is no change to a jsub script when one uses write-through cache in a farm job. Especially, there is no change in the way of specifing Auger INPUT tags to stage files from the tape library. But users need to update the cached file paths if they use the cached files directly in the farm jobs. The new cache path will not contain /mss.  For example: to get a file /mss/clas/<dir>/<filename> from tape to cache disk, its cache path will be /cache/clas/<dir>/<filename>, not /cache/mss/clas/<dir>/<filename> as in the read-only cache system.

Can a user create a hard link to another file on the /cache file system?
No. The hard link on /cache system is treated to a regular file and will be backed up to tape again. The /cache is a front end of tape system, all files on cache disk will map to a file on /mss with same path.

Can I modify a file on the cache disk after it has been backed up in the tape library?

Yes, if you want to replace a file in the tape library, use 'jcache tapeRemove cachePath' to remove it from the tape library then call 'jcache put cachePath' to back it up again. When a new file is created, there will be a  grace period of 12 days during which users can do anything with the file. After 12 days,  the file will be backed up to the tape library and is considered as a read--only file.

What is the consequence if I move a directory or a file on the cache disk if the directory or file is already in the tape library?
The cache manager will regard the moved directory and files as newly created ones. Thus, the moved directory and the file will be written to the tape library eventually. You will end up with two copies of the same content but with different names. Thus you will waste a lot of tape space (and money).  We strongly suggest not to move a file and a directory if it is already on tape.

How to back up small files on the cache disk into the tape library?
Small files are not backed up to tape because of the inefficiency of writing small files to tape. The small files will not be deleted from the cache disk within one year. If you want to put the small files into the tape library, please tar many small files together into a large tar file which will then be automatically migrated to tape.

How to allow other users in my project to retrieve files from the tape library to the directory I created?
You can use a special command jcache chmod and jcache chgrp to change group ownership and to enable group writes to the directory you created. The standard Unix command chmod and chgrp will not change ownership and permission settings on the tape library.