The Mass Storage system (also known as SAM-FS or /ms) is intended to be used for archiving research data files and storing very large files, files that are too large to fit within an individual researcher's or a department's AFS quota. Storage resources are limited; if you will need to store more than 100 gigabytes of data, you must contact Research Computing group ( research@unc.edu ) to arrange to purchase tapes for your data. Inquiries about what the current price of tapes is or any other questions regarding this process should also be emailed to Research Computing.

When storing files in mass storage, you should store a tar or zip archive instead of directories with many files. Please read the "Appropriate Use" and "Things to Avoid" lines below for what can and can't be stored in the mass storage system.

Do not use mass storage to backup your desktop hard disk. Mass storage is not to be used as a backup location for local disk drives, operating systems, or software. In general, files that change often or directories with more than a thousand files in them will cause performance problems and consume tape resources. The [ http://help.unc.edu/?id=5662 ] Iron Mountain PC backup software provided by UNC might be an alternative solution than having to copy your PC files to mass storage.

The mass storage system uses the SAM-FS software product to manage storage resources. SAM-FS is similar to an ordinary disk file system in that it keeps an inode (for recording data location, etc.) and data blocks for each file. For the user of mass storage, this file system appears to be a subdirectory of the user's AFS home directory. Files can be moved in and out of mass storage by using simple Unix/Linux commands such as cp and mv or by using sftp or scp . Note that your mass storage directory "ms" cannot be accessed directly by using the Windows AFS client. You must be logged in to a Research Computing server which has mass storage mounted.

SAM-FS is different from ordinary disk systems in that it keeps data blocks on tapes, while the inode information remains on disk. When a file is created, an inode is immediately created and the data goes to the SAM-FS disk cache. If the file stays unmodified for a few hours, it will be copied from disk cache to tape. The tape drive hardware compresses the data as it is written to tape. SAM-FS copies the data to two different tapes to ensure that we have a backup copy of every file. One tape is always on-site and one tape is stored off-site in a secure location. If problems are encountered when reading data from the on-site tape, we can still retrieve your data but it may take several work days to recall the second tape copy from off-site storage.

When the SAM-FS disk cache is 90% full, SAM-FS automatically does a release: it releases the data blocks of files that have already been written to tape until the disk cache is only 70% full. When a file that has been released is accessed it will take at least one minute for the data to be staged or brought back from tape to the disk cache.

Every 24 hours, the inodes are backed up to a location other than SAM-FS space. Therefore, if we experience a system problem related to SAM-FS, we can restore the inode table from backup. This will restore every file that was written to tape (archived) and had its inode backed up. This means the file must have been unmodified for a minimum of 24 hours to a maximum of 48 hours.

Click on the following links to learn more about Mass Storage.

We monitor the use of mass storage and will inform you if you are using it inappropriately or if you need to purchase tapes to accommodate the volume of data that you need to store.

Please read [ http://help.unc.edu/?id=4653 ] Mass Storage Common FAQs regarding the following questions useful for users new to this service.

[ http://its.unc.edu/research-computing.html ] Research Computing home page