ZFS Tunables for Lustre Metadata Servers (MDS)

Parameter	Notes	Default	Suggested
zfs_arc_max	Maximum size of the ARC.	50% RAM	75% RAM
zfs_arc_meta_limit	Increasing this value will improve performance if the workload involves operations on a large number of files and directories, or frequent metadata operations, at the cost of less file data fitting in the ARC.	25% ARC	75% ARC
zfs_vdev_scheduler	VDEV scheduler	noop	Deadline
metaslab_debug_unload	This option prevents ZFS from unloading the spacemaps from a metaslab once it is read in.	0	1
spl_kmem_cache_slab_limit	Objects of spl_kmem_cache_slab_limit or smaller will be allocated using the Linux slab allocator, large objects use the SPL allocator. A cut-off of 16K was determined to be optimal for architectures using 4K pages.	16384	16384

For a comprehensive description of all available ZFS and SPL module parameters, refer to the zfs-module-parameters(5) and spl-module-parameters(5) man pages.