On 09/02/2010 16:43, John M Ward wrote:
I don't think there is much scope for making provision for higher-capacity drives on the Iyonix. Especially with LFAU sizes, the same "law of diminishing returns" effect has now come into play as we had on the old FileCore 0.
There is scope for mitigating that. The current FileCore+ format uses up to 19 bits for IDs, this can be extended up to 24 bits with no change to the format.
Each extra ID bit doubles the size of the disc which can be used, while keeping the same wastage factors. Non shared objects are a minimum of (IDLen+1 * LFAU) bytes, and larger objects are always rounded up to the next LFAU.
The disadvantage is that for each extra bit the disc map size doubles. This leads to slower mounting times, and performance of operations which have to search or manipulate the map, such as creating, extending or deleting files are reduced.
On a 128GB disc the LFAU is 16K and minimum object size is 320K, double those for a 256GB disc. The disc map is approx 1200K in both cases.
If you increased the ID len to 22 bits, you could have a 1TB disc with an LFAU of 16K and a minimum object size of 320K just like a 128GB disc, but the map would be approximately 10MB.
When the new FileCore was introduced in RISC OS 4 some elevent years ago, not only did allow effectively unlimited filename lengths and objects per directory, it also reduced the minium LFAU size by a factor of sixteen. Now drive capacities have gone up by more than that factor, once again there is no real benefit in larger capacity drives.
No, larger drives can still hold far more data than smaller ones, you just lose an increasing fraction of it to wastage. This was always accentuated by the small size of the program and data files on RISC OS, which meant minimum object sizes and rounding was significant.
However now data sizes have increased considerably, you are only going to have so many small executable, draw and text files, the bulk of what you'll be storing on TB range discs will be large images, music and video files. In which case the wastage is an insignificant small percentage, and comparable to loses on all other formats.
Cheers ---David -- David J. Ruck email: druck@xxxxxxxxxxxx phone: +44(0)7974 108301 ---To alter your preferences or leave the group, visit //www.freelists.org/list/iyonix-support
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