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High dd with low ioping
My VPS has high dd with low ioping...what can you tell from the result? which one should I trust more? Two tests were done within 30 seconds.
dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync 16384+0 records in 16384+0 records out 1073741824 bytes (1.1 GB) copied, 8.61133 s, 125 MB/s ioping -Dc 10 . 4096 bytes from . (simfs /vz/private/2718): request=1 time=287.2 ms 4096 bytes from . (simfs /vz/private/2718): request=2 time=168.4 ms 4096 bytes from . (simfs /vz/private/2718): request=3 time=26.3 ms 4096 bytes from . (simfs /vz/private/2718): request=4 time=39.2 ms 4096 bytes from . (simfs /vz/private/2718): request=5 time=28.9 ms 4096 bytes from . (simfs /vz/private/2718): request=6 time=41.3 ms 4096 bytes from . (simfs /vz/private/2718): request=7 time=5.8 ms 4096 bytes from . (simfs /vz/private/2718): request=8 time=551.8 ms 4096 bytes from . (simfs /vz/private/2718): request=9 time=9.1 ms 4096 bytes from . (simfs /vz/private/2718): request=10 time=87.2 ms --- . (simfs /vz/private/2718) ioping statistics --- 10 requests completed in 10259.9 ms, 8 iops, 0.0 mb/s min/avg/max/mdev = 5.8/124.5/551.8/165.1 ms
Comments
dd is bad. You do not need sequential access, 99% of time. Real issue is latency.
A database will make your iowait skyrocket if it needs to wait half a second for the data... Wont need much, usually a few bits but often and sending the request then waiting for data to arrive in half a second, imagine how long will it take to generate 1 page with 100 queries, some 50 seconds if we consider only the db wait time ?
@Maounique
That io wait is terrible. But what are you doing to require 100 database queries on a page load aha
but how did it achieve high dd result with such low ioping? by hdd cache?