| Summary: | Background. One of the tasks of designing long-term electronic storage is to
minimize the number of data carriers while achieving the maximum possible reliability
of information storage. When using optical disks as media, this problem can
be solved by combining the media into RAID structures. However, for archives that
do not use expensive robotic libraries, there is a problem of rapid access to stored
information. The problem can be solved by combining media in hybrid structures,
where along with RAID arrays; information is also stored on single media. The aim
of the study is to build a mathematical model of the reliability of information storage
on optical disks combined in hybrid structures (named in the paper as G5, G6, G15,
G16), and determine the most profitable structure using this model.
Materials and methods. The model is based on well-known methods for evaluating
the reliability of RAID arrays developed for hard disks, which were supplemented
with expressions to account for the reliability of storing information on
groups of single disks. The initial data for the model is considered: the total volume
of archive storage, the capacity of a single optical disk, the probability of failure of
the optical disk during storage between integrity checks, the conditional number of
disks with information in the RAID array, and the number of spare copies being
made.
Results. A model is constructed and simulations are performed for various values
of the capacity of the electronic archive. For comparison, we also performed simulations
for RAID-based archives of the most common types (5, 6, 15, 16), as well as
for an archive based on single disks with spare copies. It is confirmed that although
hybrid structures are less reliable than "pure" RAID, they are significantly superior
to archives on single disks.
Conclusions. According to the results of the study, we can definitely recommend
the G16 structure for creating archives on optical disks combined in hybrid structures.
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