forked from Mirrors/btrfs-progs
btrfs-progs: docs: update mkfs blockgroup description
- add raid1c34 - add utilization to the overview table - wording updates Signed-off-by: David Sterba <dsterba@suse.com>master
David Sterba
parent
95117cbd4a
commit
899977cd18
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@ -28,8 +28,8 @@ mkfs.btrfs uses the entire device space for the filesystem.
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*--csum <type>*::
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*--checksum <type>*::
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Specify the checksum algorithm. Default is 'crc32c'. Valid values are 'crc32c',
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'xxhash', 'sha256' or 'blake2'. To mount such filesystem kernel must support the
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checksums as well.
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'xxhash', 'sha256' or 'blake2'. To mount such filesystem kernel must support the
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checksums as well. See 'CHECKSUM ALGORITHMS' in `btrfs`(5).
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*-d|--data <profile>*::
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Specify the profile for the data block groups. Valid values are 'raid0',
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@ -266,26 +266,28 @@ PROFILES
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There are the following block group types available:
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[ cols="^,^,^,^,^",width="60%" ]
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[ cols="<,^,^,^,>,^",width="60%" ]
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|=============================================================
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.2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Min/max devices
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.2+^.<h| Profile 3+^.^h| Redundancy .2+^.<h| Space utilization .2+^.<h| Min/max devices
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^.^h| Copies ^.^h| Parity ^.<h| Striping
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| single | 1 | | | 1/any
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| DUP | 2 / 1 device | | | 1/any ^(see note 1)^
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| RAID0 | | | 1 to N | 2/any
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| RAID1 | 2 | | | 2/any
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| RAID10 | 2 | | 1 to N | 4/any
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| RAID5 | 1 | 1 | 2 to N - 1 | 2/any ^(see note 2)^
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| RAID6 | 1 | 2 | 3 to N - 2 | 3/any ^(see note 3)^
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| single | 1 | | | 100% | 1/any
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| DUP | 2 / 1 device | | | 50% | 1/any ^(see note 1)^
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| RAID0 | | | 1 to N | 100% | 2/any
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| RAID1 | 2 | | | 50% | 2/any
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| RAID1C3 | 3 | | | 33% | 3/any
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| RAID1C4 | 4 | | | 25% | 4/any
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| RAID10 | 2 | | 1 to N | 50% | 4/any
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| RAID5 | 1 | 1 | 2 to N-1 | (N-1)/N | 2/any ^(see note 2)^
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| RAID6 | 1 | 2 | 3 to N-2 | (N-2)/N | 3/any ^(see note 3)^
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|=============================================================
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WARNING: It's not recommended to build btrfs with RAID0/1/10/5/6 profiles on
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partitions from the same device. Neither redundancy nor performance will be
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improved.
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WARNING: It's not recommended to create filesystems with RAID0/1/10/5/6
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profiles on partitions from the same device. Neither redundancy nor
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performance will be improved.
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'Note 1:' DUP may exist on more than 1 device if it starts on a single device and
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another one is added. Since version 4.5.1, *mkfs.btrfs* will let you create DUP
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on multiple devices.
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on multiple devices without restrictions.
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'Note 2:' It's not recommended to use 2 devices with RAID5. In that case,
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parity stripe will contain the same data as the data stripe, making RAID5
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@ -293,7 +295,75 @@ degraded to RAID1 with more overhead.
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'Note 3:' It's also not recommended to use 3 devices with RAID6, unless you
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want to get effectively 3 copies in a RAID1-like manner (but not exactly that).
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N-copies RAID1 is not implemented.
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'Note 4:' Since kernel 5.5 it's possible to use RAID1C3 as replacement for
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RAID6, higher space cost but reliable.
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PROFILE LAYOUT
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~~~~~~~~~~~~~~
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For the following examples, assume devices numbered by 1, 2, 3 and 4, data or
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metadata blocks A, B, C, D, with possible stripes eg. A1, A2 that would be
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logically A, etc. For parity profiles PA and QA are parity and syndrom,
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associated with the given stripe. The simple layouts single or DUP are left
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out. Actual physical block placement on devices depends on current state of
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the free/allocated space and may appear random. All devices are assumed to be
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present at the time of the blocks would have been written.
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RAID1
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[ cols="^,^,^,^",width="50%", options="header" ]
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|===
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| device 1 | device 2 | device 3 | device 4
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| A | D | |
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| B | | | C
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| C | | |
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| D | A | B |
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|===
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RAID1C3
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[ cols="^,^,^,^",width="50%", options="header" ]
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|===
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| device 1 | device 2 | device 3 | device 4
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| A | A | D |
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| B | | B |
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| C | | A | C
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| D | D | C | B
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|===
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RAID0
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[ cols="^,^,^,^",width="50%", options="header" ]
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|===
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| device 1 | device 2 | device 3 | device 4
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| A2 | C3 | A3 | C2
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| B1 | A1 | D2 | B3
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| C1 | D3 | B4 | D1
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| D4 | B2 | C4 | A4
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|===
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RAID5
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[ cols="^,^,^,^",width="50%", options="header" ]
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|===
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| device 1 | device 2 | device 3 | device 4
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| A2 | C3 | A3 | C2
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| B1 | A1 | D2 | B3
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| C1 | D3 | PB | D1
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| PD | B2 | PC | PA
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|===
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RAID6
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[ cols="^,^,^,^",width="50%", options="header" ]
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|===
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| device 1 | device 2 | device 3 | device 4
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| A2 | QC | QA | C2
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| B1 | A1 | D2 | QB
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| C1 | QD | PB | D1
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| PD | B2 | PC | PA
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|===
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DUP PROFILES ON A SINGLE DEVICE
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-------------------------------
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