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
