Add options to zfs redundant_metadata property

Currently, additional/extra copies are created for metadata in
addition to the redundancy provided by the pool(mirror/raidz/draid),
due to this 2 times more space is utilized per inode and this decreases
the total number of inodes that can be created in the filesystem. By
setting redundant_metadata to none, no additional copies of metadata
are created, hence can reduce the space consumed by the additional
metadata copies and increase the total number of inodes that can be
created in the filesystem.  Additionally, this can improve file create
performance due to the reduced amount of metadata which needs
to be written.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Dipak Ghosh <[email protected]>
Signed-off-by: Akash B <[email protected]>
Closes #13680

1 files changed, 15 insertions, 3 deletions

diff --git a/man/man7/zfsprops.7 b/man/man7/zfsprops.7
index b753ec321..1e2ca409f 100644
--- a/man/man7/zfsprops.7
+++ b/man/man7/zfsprops.7
@@ -36,8 +36,9 @@
 .\" Copyright 2018 Nexenta Systems, Inc.
 .\" Copyright 2019 Joyent, Inc.
 .\" Copyright (c) 2019, Kjeld Schouten-Lebbing
+.\" Copyright (c) 2022 Hewlett Packard Enterprise Development LP.
 .\"
-.Dd May 24, 2021
+.Dd July 21, 2022
 .Dt ZFSPROPS 7
 .Os
 .
@@ -1445,7 +1446,7 @@ affects only files created afterward; existing files are unaffected.
 .Pp
 This property can also be referred to by its shortened column name,
 .Sy recsize .
-.It Sy redundant_metadata Ns = Ns Sy all Ns | Ns Sy most
+.It Sy redundant_metadata Ns = Ns Sy all Ns | Ns Sy most Ns | Ns Sy some Ns | Ns Sy none
 Controls what types of metadata are stored redundantly.
 ZFS stores an extra copy of metadata, so that if a single block is corrupted,
 the amount of user data lost is limited.
@@ -1477,7 +1478,7 @@ When set to
 ZFS stores an extra copy of most types of metadata.
 This can improve performance of random writes, because less metadata must be
 written.
-In practice, at worst about 100 blocks
+In practice, at worst about 1000 blocks
 .Po of
 .Sy recordsize
 bytes each
@@ -1486,6 +1487,17 @@ of user data can be lost if a single on-disk block is corrupt.
 The exact behavior of which metadata blocks are stored redundantly may change in
 future releases.
 .Pp
+When set to
+.Sy some ,
+ZFS stores an extra copy of only critical metadata.
+This can improve file create performance since less metadata needs to be written.
+If a single on-disk block is corrupt, at worst a single user file can be lost.
+.Pp
+When set to
+.Sy none ,
+ZFS does not store any copies of metadata redundantly.
+If a single on-disk block is corrupt, an entire dataset can be lost.
+.Pp
 The default value is
 .Sy all .
 .It Sy refquota Ns = Ns Ar size Ns | Ns Sy none