Comment 88 for bug 607560

Ubuntu 12.04.1

Same annoying problem here. JBD2 is causing EXTREMELY high IO everytime. Next iotop sample belongs to a large file writing through NFS:

$ sudo iotop -oq

Total DISK READ: 0.00 B/s | Total DISK WRITE: 1784.50 K/s
  239 be/3 root 0.00 B/s 0.00 B/s 0.00 % 99.65 % [jbd2/sdb1-8]
 1224 be/4 root 0.00 B/s 116.89 K/s 0.00 % 1.13 % [nfsd]
 1220 be/4 root 0.00 B/s 163.64 K/s 0.00 % 0.37 % [nfsd]
 1226 be/4 root 0.00 B/s 187.02 K/s 0.00 % 0.24 % [nfsd]
 1223 be/4 root 0.00 B/s 109.10 K/s 0.00 % 0.24 % [nfsd]
 1225 be/4 root 0.00 B/s 175.33 K/s 0.00 % 0.21 % [nfsd]
 1222 be/4 root 0.00 B/s 187.02 K/s 0.00 % 0.15 % [nfsd]
 1219 be/4 root 0.00 B/s 175.33 K/s 0.00 % 0.13 % [nfsd]
 1221 be/4 root 0.00 B/s 124.68 K/s 0.00 % 0.13 % [nfsd]

The file copy started OK (80 MB/s) and, after 1 or 2 minutes, speed dropped to barely 1 MB/s. As you can see, there are no other processes doing IO at this time. This behaviour appears randomly and VERY often, not necessarily when doing net IO, so my system becomes unresponsive again and again. Other OSes behave perfectly in this machine, so it's not a hardware issue.