Re: very low performance on SCSI disks if device node is in tmpfs

[Olaf Hering]

 On Tue, May 25, Richard B. Johnson wrote unrelated stuff:

did you actually try it?

(none):~ # /usr/bin/time dd if=/dev/sdb bs=1M count=123  of=/dev/null
123+0 records in
123+0 records out
0.00user 0.75system 0:17.13elapsed 4%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps
(none):~ # /usr/bin/time dd if=/dev/sdb bs=1M count=123  of=/dev/null 
123+0 records in
123+0 records out
0.00user 0.74system 0:15.66elapsed 4%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps
(none):~ # /usr/bin/time dd if=/dev/sdb bs=1M count=123  of=/dev/null 
123+0 records in
123+0 records out
0.00user 0.78system 0:15.67elapsed 5%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps
(none):~ # /usr/bin/time dd if=/tmp/sdb bs=1M count=123  of=/dev/null 
123+0 records in
123+0 records out
0.00user 0.47system 0:06.44elapsed 7%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps
(none):~ # /usr/bin/time dd if=/tmp/sdb bs=1M count=123  of=/dev/null 
123+0 records in
123+0 records out
0.00user 0.47system 0:06.44elapsed 7%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps
(none):~ # /usr/bin/time dd if=/tmp/sdb bs=1M count=123  of=/dev/null 
123+0 records in
123+0 records out
0.00user 0.50system 0:06.44elapsed 7%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+426minor)pagefaults 0swaps


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