Want to Slow Linux ZFS Flushing/Syncing to Disk Every 5 Seconds?

So you’ve got ZFS on Linux and you notice your hard drive LED light up every 5 seconds. How can you slow that down?

The zfs_txg_timeout parameter is described as:

~# modinfo zfs |grep zfs_txg_timeout
parm:           zfs_txg_timeout:Max seconds worth of delta per txg (int)

You can check the current value of this parameter:

~# cat /sys/module/zfs/parameters/zfs_txg_timeout
5

To verify this is the parameter you want to change, set this to 10 and count the number of seconds between the hard drive light coming on:

~# echo 10 >/sys/module/zfs/parameters/zfs_txg_timeout

Once you know this is the parameter causing the hard drive activity you can tell the ZFS module the default you want it to start with on next boot by editing /etc/modprobe.d/zfs.conf and adding a line similar to the following:

options zfs zfs_txg_timeout=30

Take care when changing this number as it may result in a higher probability of lost data in the event of a power outage.