SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 10 Service Pack 2
SUSE Linux Enterprise Desktop 11
SUSE Linux Enterprise Desktop 10 Service Pack 2
How is NFS client read-ahead tuned on SLE 10 and 11?
In SLES 11, the tunable is present at:
Note that this is tunable *after* the file system is mounted. "X:Y" is variable, although with NFS it will typically be 0:something. Normally "backing devices" are block device. But for NFS, a synthetic "backing device" is created to store these parameters. In that case the 'X' is 0, and the 'Y' is some random number.
If a particular NFS mount used "0:18", then the place to tune the read ahead for that mount would be:
The system can tell you what the 0:n number through:
stat -c '%d' /mount/point
In theory, a script could be used to inspect and set the read_ahead_kb for a given file system. Here's a possible example, called set-ra.sh:
# usage: To display current value: set-ra.sh </mount/point>
# To set a new value: set-ra.sh </mount/point> <new_value>
case $# in
1) cat /sys/class/bdi/0:`stat -c '%d' "$1"`/read_ahead_kb
2) echo $2 > /sys/class/bdi/0:`stat -c '%d' "$1"`/read_ahead_kb
This script is just an example, it is not highly tested.
SLES 10 SP2:
On SLES 10 SP2, the live value is stored at /proc/sys/fs/nfs/nfs_max_readahead
For dynamic tuning, set it with (i.e. if 32 is the desired value):
echo 32 > /proc/sys/fs/nfs/nfs_max_readahead
This tunable only takes effect if it is in place before the mount is done. So to put this into effect dynamically, you'd need something in the order of:
This could also be set at boot, before /etc/fstab mounts are done, by editing /etc/sysctl.conf and adding:
fs.nfs.nfs_max_readahead = 20
However, if the system is not up-to-date, this might not come into effect during boot, due to timing issues between sysctl and nfs initialization. Without current updates (May 2009), the following may be needed after boot:
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