Comments on: ZFS - some initial testing http://dan.langille.org/2010/03/05/zfs-some-initial-testing/ He has another more popular diary. This one is more general. Fri, 18 May 2012 20:00:44 +0000 http://wordpress.org/?v=2.5 By: Arthur http://dan.langille.org/2010/03/05/zfs-some-initial-testing/#comment-541 Arthur Sat, 08 Oct 2011 12:40:36 +0000 http://dan.langille.org/?p=291#comment-541 I know this is an old post, but it should be noted that this is not a correct way to measure filesystem write-performance as /dev/urandom is oftentimes the bottleneck, not your filesystem. For some peace of mind, I just rechecked this on two basic machines (one a current fbsd, the other a mac) and raw disk write speed is anywhere between 4x and 10x faster than /dev/urandom can deliver on those machines. It's better to use /dev/zero or a script that writes semi-random data at high speed, like these 5 lines of c code; #include int main(int argc, char**argv) { unsigned char a[65003]; int i; for(i=0;i<65003;i++) a[i]=(i*31+i/256)%256; while(1) write(1,a,65003);} I know this is an old post, but it should be noted that this is not a correct way to measure filesystem write-performance as /dev/urandom is oftentimes the bottleneck, not your filesystem.

For some peace of mind, I just rechecked this on two basic machines (one a current fbsd, the other a mac) and raw disk write speed is anywhere between 4x and 10x faster than /dev/urandom can deliver on those machines.

It’s better to use /dev/zero or a script that writes semi-random data at high speed, like these 5 lines of c code;

#include
int main(int argc, char**argv) {
unsigned char a[65003]; int i;
for(i=0;i<65003;i++) a[i]=(i*31+i/256)%256;
while(1) write(1,a,65003);}

]]>