On Tuesday Martin and I installed eight more gigabytes of RAM
in our mirror server.
We have now a total of 16GB of memory and about 14GB is used for the file
system cache. This is exactly what our goal was. To decrease the number
of accesses directly on the RAID in favour of loading the files from the cache.
It would be interesting to see which parts of the files are taken from
the file system cache and what is loaded from actual disks. It is somehow hard
to tell if the memory is actually used effectively or if the 14GB for file system
cache is still not enough.
After the installation of the new DIMM modules I had to change the
IO scheduler again. For our scenario (mirror server) it is very helpful to be able
to change the IO scheduler. The default IO scheduler (cfq) is completely
useless for us and I usually change it to anticipatory on the RAIDs used
for the mirror data. For times like the Fedora 8 release I had to change it to
noop because even with anticipatory the system was not very
responsive until I changed the IO scheduler to noop.