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The Test: Comparing /dev/random speed on Linux and BSD

Date: January 6, 2012

IBM ThinkPad (1.8GHz)
DragonFly	random	129770365	bytes/sec
	urandom	79501725	bytes/sec
OpenBSD	random	92374770	bytes/sec
FreeBSD	random	35212262	bytes/sec
Debian	urandom	3576499	bytes/sec
NetBSD	urandom	1379969	bytes/sec
Single-core Dell OptiPlex (2.54GHz)
DragonFly	random	160196377	bytes/sec
	urandom	81261656	bytes/sec
OpenBSD	random	150056320	bytes/sec
FreeBSD	random	29790795	bytes/sec
Debian	urandom	2388368	bytes/sec
NetBSD	urandom	941130	bytes/sec
Gateway Solo laptop (600MHz)
DragonFly	random	39643501	bytes/sec
	urandom	20024305	bytes/sec
OpenBSD	random	28902905	bytes/sec
FreeBSD	random	10608869	bytes/sec
Debian	urandom	1002416	bytes/sec
NetBSD	urandom	421040	bytes/sec

Operating systems tested:

DragonFly BSD 2.10.1 i386
OpenBSD 5.0 i386
FreeBSD 8.2 i386
Debian GNU/Linux 6.0.3 i386
NetBSD 5.1 i386

Methodology: I downloaded and burned ISO installation images for DragonFly, FreeBSD, Debian, and NetBSD, and used my existing (official release) OpenBSD CDs to perform fresh, bare-metal installs on three different computers: a 1.8GHz IBM ThinkPad, a 2.54GHz Dell OptiPlex, and a 600MHz Gateway Solo. No VMs were used, and default installation parameters were accepted. (Only non-default choice: The UFS filesystem was chosen over HAMMER on DragonFly, given the small disks of the test machines.) I rebooted each machine after installation, logged in, and ran dd if=/dev/random bs=32k of=/dev/null, experimenting with different blocksize values before picking the fastest in each case. I then ran dd, using the count parameter in conjunction with the blocksize to write an equal number of bytes for each OS to /dev/null, thereby getting the purest numbers on /dev/random device speed. /dev/random speed comparison
of BSD and Linux

Discussion: DragonFly has the highest /dev/random performance with OpenBSD following close behind. The /dev/random devices on DragonFly and OpenBSD are so fast that when wiping drives on these test machines, /dev/zero would not offer a performance improvement over /dev/random, as the disk itself is the limiting factor.

Please note that:

On OpenBSD, all /dev/*random devices use the same code.
On FreeBSD, /dev/urandom is a symlink to /dev/random.
On Linux and NetBSD, /dev/random was too slow to record useful data and so /dev/urandom was chosen.
On DragonFly BSD, /dev/random is inexplicably faster than /dev/urandom. This contradicts the current (as of Jan. 6, 2012) random(4) manual page which states that "The /dev/urandom device uses a different and much faster algorithm, but one which is not considered to be as secure (though for all practical purposes it probably is good enough)."