Disk write speed drops to zero in 16.04, but not in 14.04
I'm using a Dell R410 2x Xeon E5620, 24GB RAM, 2x2TB 7200rpm, disk controller is a PERC H200, hardware RAID0. Ubuntu server 16.04 fresh install fully updated.
Problem: When writing a constant speed of 100MB/s, write speed drops to 0MB/s once every 20-25 second.
At first I thought that I had defective hard drives, but SMART-status check is OK. Still thought something was wrong with hard drives, since this behavior is not normal.
Double-check disk controller:
Disk Cache Policy : Enabled
I decided to test a 10G file with wget (from local server) -> https:/
This gif shows the problem pretty clearly. Same wget with -O /dev/null, rock solid 110MB/s the whole 10G.
Next test with a dd:
dd if=/dev/zero of=test bs=64k count=256k conv=fdatasync
17179869184 bytes (17 GB) copied, 61.1649 s, 281 MB/s
OK, that seems fine. Whats going on?
with iotop during "dd if=/dev/zero of=test bs=64k count=256k conv=fdatasync" -> https:/
Wait what, look at top right corner: "Total DISK WRITE:", that doesn't seem healthy! Jumping around in speed with an "base average" of 30-40MB/s. Should be a steady average of 280MB/s!
wget to RAM, no problem.
wget to disk, problem.
I'm just guessing it's disk-related. It. must. be.
I kind of accidentally re-install the whole system with 14.04 instead of 16.04, and what do you know, everything is working just as it should!
Top right corner: "Total DISK WRITE:"
wget 10G file 110MB/s to disk rock solid, no dips at all.
What is going on? Seems to be a Linux/kernel/driver related problem? I tried re-install 16.04, same problem occurs again, back to 14.04, working just fine.
Can you help with this problem?
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