This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
This is a complicated question to answer with any hard and fast rules. For starters the media and filing system being used must be considered. If you are using an IDE drive under ADFS then you usually should have your drive formatted as one whole partition due to ADFS' inability to support multiple partitions. (Although third party extensions, like Alsystems PowerIDE software, can extend the default IDE interface to include partioning.) However this is not always true and sometimes it can be beneficial to sacrifice a few Mbs of partition size to gain tens of Mb savings in red uced space wastage when storing files.
RISC OS uses, and through FileCore virtually all filing systems share this, a fairly complicated map system that tries to make a reasonable compromise between filing system overheads, speed and flexibility. For drives 512Mb or less this system works quite well. With the advent of easily available multiple Gb size drives the system begins to suffer a little.
For reasons that are beyond the scope of the FAQ to explain RISC OS links the LFAU (Large File Allocation Unit) to the minimum object size on a disc by a ratio of sixteen to one. Thus a two byte sized file occupies a minimum of sixteen kilobytes of actual disc space to store. There is an important exception to this involving the sharing of map entries, and thus disc space, but the general rule is as above. This table summarises the relationship between LFAU, disc size and minimum object size.
lfau max disc size min object ---- ------------- ---------- 1K 499M bytes 16kb 2K 998M bytes 32kb 4K 1996M bytes 64kb 8K 3992M bytes 128kb
Consequently it can be easily seen that the larger the partition size the larger the individual file overheads of storing it becomes. (NB It is worth pointing out that Image Filing systems do not share this overhead directly.)
Thus which partition size you should aim for depends on what you intend doing with the drive. If you are primarily storing Replay films then given the multi-megabyte size of the files the overheads required for storing each file is percentage wise less and it is more important to have bulk disc storage available than it is efficiency of space utilisation. On the other hand running a news spool will involve thousands of files averaging around the seven kilobyte mark, thus a smaller partition size will great ly reduce space wastage to filing system overheads.
In the FAQ maintainers experience a good compromise size seems to be the just sub one gigabyte mark.