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High dd with low ioping
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High dd with low ioping

CoolMoonCoolMoon Member

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


  • 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?

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