For what it is worth, I too have seen this behavior when load testing our zfs
box. I used iometer and the RealLife profile (1 worker, 1 target, 65% reads,
60% random, 8k, 32 IOs in the queue). When writes are being dumped, reads drop
close to zero, from 600-700 read IOPS to 15-30 read IOPS.
zpool iostat data01 1
Where data01 is my pool name
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
data01 55.5G 20.4T 691 0 4.21M 0
data01 55.5G 20.4T 632 0 3.80M 0
data01 55.5G 20.4T 657 0 3.93M 0
data01 55.5G 20.4T 669 0 4.12M 0
data01 55.5G 20.4T 689 0 4.09M 0
data01 55.5G 20.4T 488 1.77K 2.94M 9.56M
data01 55.5G 20.4T 29 4.28K 176K 23.5M
data01 55.5G 20.4T 25 4.26K 165K 23.7M
data01 55.5G 20.4T 20 3.97K 133K 22.0M
data01 55.6G 20.4T 170 2.26K 1.01M 11.8M
data01 55.6G 20.4T 678 0 4.05M 0
data01 55.6G 20.4T 625 0 3.74M 0
data01 55.6G 20.4T 685 0 4.17M 0
data01 55.6G 20.4T 690 0 4.04M 0
data01 55.6G 20.4T 679 0 4.02M 0
data01 55.6G 20.4T 664 0 4.03M 0
data01 55.6G 20.4T 699 0 4.27M 0
data01 55.6G 20.4T 423 1.73K 2.66M 9.32M
data01 55.6G 20.4T 26 3.97K 151K 21.8M
data01 55.6G 20.4T 34 4.23K 223K 23.2M
data01 55.6G 20.4T 13 4.37K 87.1K 23.9M
data01 55.6G 20.4T 21 3.33K 136K 18.6M
data01 55.6G 20.4T 468 496 2.89M 1.82M
data01 55.6G 20.4T 687 0 4.13M 0
-Scott
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