Re: raid and cgd

[Alexander Nasonov <alnsn%yandex.ru@localhost>]

Edgar Fu? wrote:
> 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.

Your description matches a paragraph in raidctl(8) that starts with
'Tuning RAID 5 sets is trickier.' while my setup is RAID 1 and
recommended values for SectPerSU are 32 to 128. I set it to 128 but
I'll try 64 to see if makes a difference.

-- 
Alex