Setting up the Archive Server cache space

An Archive Server always has a cache. A cache is a set of directories on the hard disks where images are kept until they are copied onto archive media. When images are retrieved from archive media, the data is first copied to the cache before it is transmitted to a display station.

Cache space

You must determine the correct amount of disk space to reserve for the cache on the Archive Server. The size of the cache, divided by the daily volume of image data determines how many days worth of exams are available for immediate display from the archive cache. The goal is to have enough cache space for several days of exams, so that users do not have to retrieve studies from the archive media. Use the following calculation to determine the cache size:

total raw disk space = (D+P)*N*F*U, where:

Variable	Represents
D	Amount of new data produced during one working day.
P	Average amount of prefetched image data for one working day. Prefetch refers to retrieving priors or relevant priors to cache based on scheduled exams for that day.
N	Number of days worth of data that can exist in the cache. For example, if you require the past four days worth of data in cache, N=4.
F	Fudge factor of 1.3 to allow for normal workload variations.
U	UNIX file system overhead of 1.1.