FILESYSTEM FEATURES
-------------------
+Features that can be enabled during creation time. See also `btrfs`(5) section
+'FILESYSTEM FEATURES'.
+
*mixed-bg*::
+(kernel support since 2.6.37)
++
mixed data and metadata block groups, also set by option '--mixed'
*extref*::
sizes that can be stored into one metadata block
*raid56*::
+(kernel support since 3.9)
++
extended format for RAID5/6, also enabled if raid5 or raid6 block groups
are selected
reduced-size metadata for extent references, saves a few percent of metadata
*no-holes*::
+(kernel support since 3.14)
++
improved representation of file extents where holes are not explicitly
stored as an extent, saves a few percent of metadata if sparse files are used
.2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Min/max devices
^.^h| Copies ^.^h| Parity ^.<h| Striping
| single | 1 | | | 1/any
-| DUP | 2 / 1 device | | | 1/any ^(see note)^
+| DUP | 2 / 1 device | | | 1/any ^(see note 1)^
| RAID0 | | | 1 to N | 2/any
| RAID1 | 2 | | | 2/any
| RAID10 | 2 | | 1 to N | 4/any
-| RAID5 | 1 | 1 | 2 to N - 1 | 2/any
-| RAID6 | 1 | 2 | 3 to N - 2 | 3/any
+| RAID5 | 1 | 1 | 2 to N - 1 | 2/any ^(see note 2)^
+| RAID6 | 1 | 2 | 3 to N - 2 | 3/any ^(see note 3)^
|=============================================================
-'Note:' DUP may exist on more than 1 device if it starts on a single device and
+WARNING: It's not recommended to build btrfs with RAID0/1/10/5/6 prfiles on
+partitions from the same device. Neither redundancy nor performance will be
+improved.
+
+'Note 1:' DUP may exist on more than 1 device if it starts on a single device and
another one is added. Since version 4.5.1, *mkfs.btrfs* will let you create DUP
on multiple devices.
+'Note 2:' It's not recommended to use 2 devices with RAID5. In that case,
+parity stripe will contain the same data as the data stripe, making RAID5
+degraded to RAID1 with more overhead.
+
+'Note 3:' It's also not recommended to use 3 devices with RAID6, unless you
+want to get effectively 3 copies in a RAID1-like manner (but not exactly that).
+N-copies RAID1 is not implemented.
+
DUP PROFILES ON A SINGLE DEVICE
-------------------------------
SEE ALSO
--------
-`btrfs`(8), `wipefs`(8)
+`btrfs`(5),
+`btrfs`(8),
+`wipefs`(8)