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btrfs-progs: docs: update mkfs blockgroup description

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- add raid1c34
- add utilization to the overview table
- wording updates

Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2019-11-15 16:14:50 +01:00
parent 95117cbd4a
commit 899977cd18
1 changed files with 86 additions and 16 deletions
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102
Documentation/mkfs.btrfs.asciidoc
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@ -28,8 +28,8 @@ mkfs.btrfs uses the entire device space for the filesystem.
*--csum <type>*::
*--checksum <type>*::
Specify the checksum algorithm. Default is 'crc32c'. Valid values are 'crc32c',
'xxhash', 'sha256' or 'blake2'. To mount such filesystem kernel must support the
checksums as well.
'xxhash', 'sha256' or 'blake2'. To mount such filesystem kernel must support the
checksums as well. See 'CHECKSUM ALGORITHMS' in `btrfs`(5).
*-d|--data <profile>*::
Specify the profile for the data block groups. Valid values are 'raid0',
@ -266,26 +266,28 @@ PROFILES
There are the following block group types available:
[ cols="^,^,^,^,^",width="60%" ]
[ cols="<,^,^,^,>,^",width="60%" ]
|=============================================================
.2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Min/max devices
.2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Space utilization .2+^.<h| Min/max devices
^.^h| Copies ^.^h| Parity ^.<h| Striping
| single | 1 | | | 1/any
| 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 ^(see note 2)^
| RAID6 | 1 | 2 | 3 to N - 2 | 3/any ^(see note 3)^
| single | 1 | | | 100% | 1/any
| DUP | 2 / 1 device | | | 50% | 1/any ^(see note 1)^
| RAID0 | | | 1 to N | 100% | 2/any
| RAID1 | 2 | | | 50% | 2/any
| RAID1C3 | 3 | | | 33% | 3/any
| RAID1C4 | 4 | | | 25% | 4/any
| RAID10 | 2 | | 1 to N | 50% | 4/any
| RAID5 | 1 | 1 | 2 to N-1 | (N-1)/N | 2/any ^(see note 2)^
| RAID6 | 1 | 2 | 3 to N-2 | (N-2)/N | 3/any ^(see note 3)^
|=============================================================
WARNING: It's not recommended to build btrfs with RAID0/1/10/5/6 profiles on
partitions from the same device. Neither redundancy nor performance will be
improved.
WARNING: It's not recommended to create filesystems with RAID0/1/10/5/6
profiles 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.
on multiple devices without restrictions.
'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
@ -293,7 +295,75 @@ 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.
'Note 4:' Since kernel 5.5 it's possible to use RAID1C3 as replacement for
RAID6, higher space cost but reliable.
PROFILE LAYOUT
~~~~~~~~~~~~~~
For the following examples, assume devices numbered by 1, 2, 3 and 4, data or
metadata blocks A, B, C, D, with possible stripes eg. A1, A2 that would be
logically A, etc. For parity profiles PA and QA are parity and syndrom,
associated with the given stripe. The simple layouts single or DUP are left
out. Actual physical block placement on devices depends on current state of
the free/allocated space and may appear random. All devices are assumed to be
present at the time of the blocks would have been written.
RAID1
[ cols="^,^,^,^",width="50%", options="header" ]
|===
| device 1 | device 2 | device 3 | device 4
| A | D | |
| B | | | C
| C | | |
| D | A | B |
|===
RAID1C3
[ cols="^,^,^,^",width="50%", options="header" ]
|===
| device 1 | device 2 | device 3 | device 4
| A | A | D |
| B | | B |
| C | | A | C
| D | D | C | B
|===
RAID0
[ cols="^,^,^,^",width="50%", options="header" ]
|===
| device 1 | device 2 | device 3 | device 4
| A2 | C3 | A3 | C2
| B1 | A1 | D2 | B3
| C1 | D3 | B4 | D1
| D4 | B2 | C4 | A4
|===
RAID5
[ cols="^,^,^,^",width="50%", options="header" ]
|===
| device 1 | device 2 | device 3 | device 4
| A2 | C3 | A3 | C2
| B1 | A1 | D2 | B3
| C1 | D3 | PB | D1
| PD | B2 | PC | PA
|===
RAID6
[ cols="^,^,^,^",width="50%", options="header" ]
|===
| device 1 | device 2 | device 3 | device 4
| A2 | QC | QA | C2
| B1 | A1 | D2 | QB
| C1 | QD | PB | D1
| PD | B2 | PC | PA
|===
DUP PROFILES ON A SINGLE DEVICE
-------------------------------