On-Line, Near-Line, and Off-Line |
On-line storage is the local hard drive or continuously spinning
cd-rom. On-line storage allows for the easiest and quickest access to data.
The average personal computer now comes with more than a gigabyte of storage,
and upgrades are not very expensive. Unfortunately, hard drive space is
often limited and crowded, and requires a great deal of ongoing organization
to manage. Data on the hard drive is simply moved by anyone with the proper
access. A clear directory structure and clear procedures for subdirectories
must be adhered to by everyone who writes to the hard dirve. Without a
great deal of organization and policing, a hard drive can quickly become
a tangle of files.
Near-line storage is usually described as a system of automated,
and not necessarily local, data retrieval. Using tapes or cd-roms, and
sometimes robotics, data is written to storage devices and retrieved and
rewritten to the hard drive only when recalled by a user. Although it may
require a few extra moments to retrieve the data, many near-line storage
facilities are faster than the average cd-rom drive. The process can be
totally seamless to the user. After requesting the data, the user may replace
the data in the storage facility, or leave it on the hard drive for further
manipulation. Really efficient near-line mechanisms will move any data
that has not been recently accessed to the storage site automatically.
Near-line facilities are usually expensive and are most often developed
and maintained by computing centers for the entire university or company.
Because of the number of different users and files maintained by a computer
center, such facilities usually have well organized directories and file
structures into which the library’s data can be easily inserted and retrieved.
The library may gain storage space with little overhead and maintenance
required.
Off-line storage are usually cd-roms, floppy disks, or magnetic
tape on shelves or in other manual storage sites. These are probably the
least expensive storage options, but also the least efficient. Libraries
in the US have seen an huge increase in the amount of data distributed
on cd-rom, and now we must manage hundreds if not thousands of disks. It
requires human intervention to locate and retrieve the data. Off-site users
in particular are at a disadvantage. At PSU we offer to place off-line
data in an ftp directory for a day for remote users to download, but this
requires a great deal of staff time. Off-line storage does however provide
unlimited amounts of storage. The number of cds or magnetic tapes will
be limited by physical rather than virtual space.
In reality, most data providers use a combination of storage solutions.
Heavily used data is kept on-line, data not frequently used is kept near-line
and older, archived or little used data is kept off-line. At PSU we have
filled our hard drive, are managing thousands of cd-roms. We concentrate
on providing on-line access to data concerning Pennsylvania.
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Suggested Citation |
Lamont, Melissa, "Digital Map Librarianship: Library Functions; Storage."
Digital Map Librarianship: a working syllabus, 63rd IFLA Conference, Copenhagen,
Denmark. (4, Sept. 1997) <http://magic.lib.uconn.edu/ifla/lb_st.htm>
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