The current defaults are causing 15 MB readaheads for NFS, which are extremely large and cause excessive traffic and lags. To see the issue: Mount an NFS dir using the defaults: # mount -t nfs localhost:/srv/ltsp /mnt See the defaults (i.e. rsize=1M): # grep /mnt /proc/mounts localhost:/srv/ltsp /mnt nfs4 rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=127.0.0.1,local_lock=none,addr=127.0.0.1 0 0 Find the DEV number: # cat /proc/fs/nfsfs/volumes NV SERVER PORT DEV FSID FSC v4 7f000001 801 0:67 3f3a98a25a94496f:bd99243e3e0529bd no See the resulting read_ahead_kb kernel variable: # cat /sys/devices/virtual/bdi/0:67/read_ahead_kb 15360 I.e. the kernel will try to read ahead up to 15 MB for each opened file, resulting in excessive traffic and lags. For example, netbooting an ext4-over-nfs client with the default results in 1160 MB traffic, while with `echo 4 > /sys/devices/virtual/bdi/0:67/read_ahead_kb` (on the client) it results in 221 MB traffic, and that way it boots a lot faster and without lags. Non-NFS devices default to read_ahead_kb of 128K: cat /sys/devices/virtual/bdi/*/read_ahead_kb 128 Initially, NFS_MAX_READAHEAD=15 was used along with rsize=512 to *lower* that read_ahead_kb to 7 (KB) for NFS, as 128 KB is too big for NFS. Now with rsize=1M, it's causing read aheads of 15 MB which are clearly too large. Thank you, Alkis Georgopoulos