diff options
| author | Qu Wenruo <quwenruo@cn.fujitsu.com> | 2016-09-06 17:35:06 +0200 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2016-09-21 11:47:31 +0200 |
| commit | 53c4e289c237e4f1008fdec54256e81c24c8882a (patch) | |
| tree | 0fd4f494f50d58b141f762078a9fa520fd63378a /Documentation/mkfs.btrfs.asciidoc | |
| parent | c2f3212502210427c5f17e66fbb30ad89826fbd7 (diff) | |
btrfs-progs: mkfs: Warn user for minimal RAID5/6 devices setup
For RAID5, 2 devices setup is just RAID1 with more overhead.
For RAID6, 3 devices setup is RAID1 with 3 copies, not what most user
want.
So warn user at mkfs time for such case, and add explain in man pages.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'Documentation/mkfs.btrfs.asciidoc')
| -rw-r--r-- | Documentation/mkfs.btrfs.asciidoc | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc index 98fe694b..7d19a146 100644 --- a/Documentation/mkfs.btrfs.asciidoc +++ b/Documentation/mkfs.btrfs.asciidoc @@ -263,18 +263,26 @@ There are the following block group types available: .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 +'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 ------------------------------- |