Re: OBSD is fast!

[Seth Arnold <sarnold@willamette.edu>]

* Rakhesh Sasidharan <rakhesh@cse.iitd.ernet.in> [010124 03:13]:
> I wouldn't know if  OpenBSD carried out the copying actions as fast as it
> could have, but I do know that it was quite responsive under the load.  Is
> there any specific reason for such a difference between the two systems,
> or did  it just happen thus ?

Well, Linux handles disk caching differently than OpenBSD (likely all
*BSD) -- Linux uses dynamic buffers and caches to read and write from
the drive. An operation such as this is liable to chew through all your
memory in no real productive way.

OpenBSD uses a fixed amount of buffers and caches for disk access -- as
such, an operation such as this is not going to use all your memory. It
will use only a small fragment of your memory.

Thus, other processes will remain more responsive, as the OS doesn't
need to fault in new pages from swap space to fufill their memory requests.

I must admit, I too am surprised at how poorly your Linux machine
handled -- mine never seem to get that bad, though I have done similar
operations. (Look into hdparm for a possible way of helping the
situation improve.)

A last comment -- I *never* copy from two partitions or to two
partitions -- the poor little swing arm in the drive will end up
traversing a *lot* more space, taking ~4ms or so each seek. I think if
you do one partition at a time, you may notice speed increases in the
overall progress.

HTH

-- 
``Oh Lord; Ooh you are so big; So absolutely huge; Gosh we're all
really impressed down here, I can tell you.''