Low HDD tranfer rate with FreeBSD 5.3-Release

Dan Nelson dnelson at allantgroup.com
Mon May 9 12:50:21 PDT 2005


In the last episode (May 09), Amandeep said:
> Amandeep wrote:
> >>>>>>The transfer rate is about 15MB/s
> >>>>>>
> >>>>>>when I run
> >>>>>>#dd if=/dev/zero of=/usr/junk bs=8192
> >
> >OK with the above dd
> >
> >dd if=/dev/ad0 of=/dev/null bs=64k
> >
> >it gives me 56MB/s. from the start.
> 
> So how does the block size makes the difference?? What is the true 
> transfer rate.?

At the moment, 56MB/sec :)

Those two speeds aren't directly comparable, since your first was
testing writes through the filesystem with a small blocksize, and the
second was testing reads to the raw device with a large blocksize. 
Usually reading, using raw devices, and using large blocksizes are
faster then writing, using a filesystem, and using small blocksizes, so
all three changes probably contributed a little to the speed
difference.

-- 
	Dan Nelson
	dnelson at allantgroup.com


More information about the freebsd-questions mailing list