I have recently done some performance tests on a new server (using dd) and wonder why read performance is so much worse than write performance? Shouldn't it be another way around?
file size was in both tests 550GB, read: in seconds: 3704 in MB/s: 148
and write: in seconds: 1539 in MB/s: 357
time sh -c "dd if=/dev/zero of=/local/postgresql/bigfile bs=8k count=67108864 && sync"
time dd if=/local/postgresql/bigfile of=/dev/null bs=8k
bash time command output:
real: 61m44.335s user: 0m12.721s sys: 10m35.884s
Bonnie++ results command:
bonnie++ -f -D -n 0 -u root -d /local/postgresql/
results are for file that was twice as big as RAM size.
419 918 K/sec
~ 187 000 K/sec