2006/1/18, Mario 'BitKoenig' Holbe [off-list ref]:

Mario 'BitKoenig' Holbe [off-list ref] wrote:

quoted

scheduled read-requests. Would it probably make sense to split one
single read over all mirrors that are currently idle?

A I got it from the other thread - seek times :)
Perhaps using some big (virtual) chunk size could do the trick? What
about using chunks that big that seeking is faster than data-transfer...
assuming a data rate of 50MB/s and 9ms average seek time would result in
at least 500kB chunks, 14ms average seek time would result in at least
750kB chunks.
However, since the blocks being read are most likely somewhat close
together, it's not a typical average seek, so probably smaller chunks
would also be possible.


regards
  Mario

Stop me if I'm wrong, but this is called... huge readahead. Instead of
reading 32k on drive0 then 32k on drive1, you read continuous 512k
from drive0 (16*32k) and 512k from drive1, resulting in a 1M read.
Maybe for a single 4k page...

So my additionnal question to this would be : how well does md fit
with linux's/fs readahead policies ?