Re: raid and cgd

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> Can you please elaborate? Do they have to match for the best performance,
> or should one be a multiple of the other?
RAIDframe operates on units called stripes. FFS mostly operates on FS blocks. 
If one FS block is not exactly a whole number of stripes (either because of 
misalignment or because an FS block is smaller than a RAID stripe), then each 
write of an FS block will force the RAID to do a RMW cycle.
Further down, RAIDframe will operate on the components in units of stripe size 
divided by (components minus one). If this is not aligned to whatever the 
component can natively modify (think 512e discs), then the component will RMW.
Doing RMW will dramatically (at least by a factor of three, more likely ten) 
reduce performance.