disk IO very low on debian 9.9 with kernel 4.9.0-9
Hello all,
We recently found out that disk IO were very low when running debian
9.9 with the actual kernel 4.9.0-9.
For example when we run this command:
dd if=/dev/zero of=test bs=512 count=1000 oflag=dsync
our tests show results between 40kB/s and 70kB/s at the best.
We initially noticed those bad scores on our VMWare ESXi 6.0 and 6.7
platform (with a full flash SAN), but when we performed the same test
on Hyper-V or Virtualbox on a PC (with SSD disk) the results were more
or less the same (even worst for one them).
The same test performed on a debian testing (with kernel 4.19.0-5)
gives us scores between 200 and 400kB/s (the lowest was on my laptop
with Virtualbox).
We tried too on other linux distrib (unfortunately not with close
version of kernel) and we usually got at least 50% more than the best
score on debian testing :(
After I compiled a new kernel for the debian 9.9 (4.19.37 from debian
kernel source and 4.20.9 from kernel.org) I got results between 120
and 160kB/s.
You can see the results below:
root@debian9:/boot# cat /etc/debian_version && uname -sr && dd
if=/dev/zero of=test3 bs=512 count=1000 oflag=dsync
9.9
Linux 4.20.9-amd64
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 3.37676 s, 152 kB/s
root@debian9:/boot# cat /etc/debian_version && uname -sr && dd
if=/dev/zero of=test3 bs=512 count=1000 oflag=dsync
9.9
Linux 4.19.37-amd64
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 4.09023 s, 125 kB/s
root@debian9:~# cat /etc/debian_version && uname -sr && dd
if=/dev/zero of=test3 bs=512 count=1000 oflag=dsync
9.9
Linux 4.9.0-9-amd64
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 11.9743 s, 42.8 kB/s
We didn't have time yet to install a debian 9.9 directly on a computer
or a physical server directly to check if it could be linked to the
virtualization, but we might give it a try next week.
So did anyone of you encountered the same problem or know why it happens?
Many Thanks,
Regards,
Alexandre
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