Red Hat Bugzilla – Bug 788716
Write-perf reports useless results due to use of /dev/urandom
Last modified: 2013-07-24 14:01:43 EDT
Contrary to popular belief, urandom is not free. In generic testing, a simple dd using /dev/urandom performs at about half the performance compared to /dev/zero for fully synchronous I/O, about 1/20 for buffered I/O (i.e. the difference on the input side is mostly masked when waiting for disks on the output side). There's probably we can do about read-perf without platform-specific flushing of kernel buffers, but for write-perf we can at least get more accurate and useful numbers by using /dev/zero instead.
CHANGE: http://review.gluster.com/2728 (Use /dev/zero instead of /dev/urandom to get realistic numbers.) merged in master by Anand Avati (firstname.lastname@example.org)