[Gllug] dd and iotop weirdness

[t.clarke]

Out of interest (its probably not relevant); does dd to a disk to raw i-o
straight to the disc or is it buffered through the O-S?   I know that with Unix
you get the choice of a block(buffered) device or character(raw) device and
usage of one or the other makes a difference.   Personally, I found the only
reliable way of testing i-o speed in these circumstances is to dd n number of
1000k (eg) blocks and check the 'wall time' used to complete.   Of course,
if the o-s is still syncing the disc when dd completes the timing will be off -
just look at the pretty lights on the drives if they have them :-)

Tim
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