Viewing: lod.mirror_count_max.4
.TH LOD.MIRROR_COUNT_MAX 4 2026-02-20 Lustre "Lustre Kernel Interfaces"
.SH NAME
lod.mirror_count_max \- maximum number of mirrors allowed per file
.SH SYNOPSIS
.SY
.BI "lctl get_param lod." FSNAME "*.mirror_count_max"
.SY
.BI "lctl set_param lod." FSNAME "*.mirror_count_max=" NUM_MIRRORS
.YS
.SS PROPERTIES
.TP
.B Perms
.br
.BR 644 " | " -rw-r--r--
.TP
.B Scope
.br
Per-MDT
.TP
.B Config
.br
Always present on MDS nodes
.TP
.B Default
.br
.RB lod.*.mirror_count_max= 16
.TP
.B Limits
.br
.RB lod.*.mirror_count_max= 0
.br
.RB lod.*.mirror_count_max= 256
.SH DESCRIPTION
.B mirror_count_max
controls the maximum number of mirrors that the MDS allows to be created
on a single file via
.BR "lfs mirror create" .
.PP
The default limit of 16 mirrors matches the previous hard-coded maximum.
This limit is somewhat arbitrary and is not imposed by any on-disk format
restriction. In practice, the number of layout components in a single
file is limited to about 512 single-stripe components due to the maximum
.B trusted.lov
xattr size of 65536 bytes (VFS
.BR XATTR_SIZE_MAX ),
so 256 mirrors is a realistic upper limit today if the stripe count or
component count is more than 1.
.PP
The
.I NUM_MIRRORS
parameter accepts values from 0 (disables FLR mirroring) to
.B LUSTRE_MIRROR_COUNT_MAX
(currently 256).
.SH EXAMPLES
Increase the mirror limit to 256 on all MDTs for the
.B testfs
filesystem:
.EX
.RB "mds# " "lctl set_param lod.testfs-*.mirror_count_max=256"
.EE
.SH AVAILABILITY
.B mirror_count_max
is part of the
.BR lustre (7)
filesystem package since release 2.18.0.
.\" Added in commit 2.17.51.xxx
.SH SEE ALSO
.BR lfs-mirror-create (1),
.BR lfs-mirror-extend (1),
.BR lfs-setstripe (1),
.BR lctl-get_param (8),
.BR lctl-set_param (8)
