6 btrfs-balance - balance block groups on a btrfs filesystem
10 *btrfs balance* <subcommand> <args>
14 The primary purpose of the balance feature is to spread block groups across
15 all devices so they match constraints defined by the respective profiles. See
16 `mkfs.btrfs`(8) section 'PROFILES' for more details.
17 The scope of the balancing process can be further tuned by use of filters that
18 can select the block groups to process. Balance works only on a mounted
21 The balance operation is cancellable by the user. The on-disk state of the
22 filesystem is always consistent so an unexpected interruption (eg. system crash,
23 reboot) does not corrupt the filesystem. The progress of the balance operation
24 is temporarily stored and will be resumed upon mount, unless the mount option
25 'skip_balance' is specified.
27 WARNING: running balance without filters will take a lot of time as it basically
28 rewrites the entire filesystem and needs to update all block pointers.
30 The filters can be used to perform following actions:
32 - convert block group profiles (filter 'convert')
33 - make block group usage more compact (filter 'usage')
34 - perform actions only on a given device (filters 'devid', 'drange')
36 The filters can be applied to a combination of block group types (data,
37 metadata, system). Note that changing 'system' needs the force option.
39 NOTE: the balance operation needs enough work space, ie. space that is
40 completely unused in the filesystem, otherwise this may lead to ENOSPC reports.
41 See the section 'ENOSPC' for more details.
46 NOTE: The balance subcommand also exists under the *btrfs filesystem*
47 namespace. This still works for backward compatibility but is deprecated and
48 should not be used anymore.
50 NOTE: A short syntax *btrfs balance <path>* works due to backward compatibility
51 but is deprecated and should not be used anymore. Use *btrfs balance start*
57 cancel running or paused balance
60 pause running balance operation, this will store the state of the balance
61 progress and used filters to the filesystem
64 resume interrupted balance
66 *start* [options] <path>::
67 start the balance operation according to the specified filters, no filters
68 will rewrite the entire filesystem. The process runs in the foreground.
73 act on data block groups, see `FILTERS` section for details about 'filters'
75 act on metadata chunks, see `FILTERS` section for details about 'filters'
77 act on system chunks (requires '-f'), see `FILTERS` section for details about 'filters'.
79 be verbose and print balance filter arguments
81 force reducing of metadata integrity, eg. when going from 'raid1' to 'single'
83 *status* [-v] <path>::
84 Show status of running or paused balance.
86 If '-v' option is given, output will be verbose.
90 From kernel 3.3 onwards, btrfs balance can limit its action to a subset of the
91 full filesystem, and can be used to change the replication configuration (e.g.
92 moving data from single to RAID1). This functionality is accessed through the
93 '-d', '-m' or '-s' options to btrfs balance start, which filter on data,
94 metadata and system blocks respectively.
96 A filter has the following structure: 'type'[='params'][,'type'=...]
98 The available types are:
100 *profiles=<profiles>*::
101 Balances only block groups with the given profiles. Parameters
102 are a list of profile names separated by "'|'" (pipe).
106 Balances only block groups with usage under the given percentage. The
107 value of 0 is allowed and will clean up completely unused block groups, this
108 should not require any new work space allocated. You may want to use 'usage=0'
109 in case balance is returning ENOSPC and your filesystem is not too full.
111 The argument may be a single value or a range. The single value 'N' means 'at
112 most N percent used', equivalent to '..N' range syntax. Kernels prior to 4.4
113 accept only the single value format.
114 The minimum range boundary is inclusive, maximum is exclusive.
117 Balances only block groups which have at least one chunk on the given
118 device. To list devices with ids use *btrfs fi show*.
121 Balance only block groups which overlap with the given byte range on any
122 device. Use in conjunction with 'devid' to filter on a specific device. The
123 parameter is a range specified as 'start..end'.
126 Balance only block groups which overlap with the given byte range in the
127 filesystem's internal virtual address space. This is the address space that
128 most reports from btrfs in the kernel log use. The parameter is a range
129 specified as 'start..end'.
131 *convert=<profile>*::
132 Convert each selected block group to the given profile name identified by
135 NOTE: starting with kernel 4.5, the 'data' chunks can be converted to/from the
136 'DUP' profile on a single device.
140 Process only given number of chunks, after all filters are applied. This can be
141 used to specifically target a chunk in connection with other filters ('drange',
142 'vrange') or just simply limit the amount of work done by a single balance run.
144 The argument may be a single value or a range. The single value 'N' means 'at
145 most N chunks', equivalent to '..N' range syntax. Kernels prior to 4.4 accept
146 only the single value format. The range minimum and maximum are inclusive.
149 Balance only block groups which have the given number of stripes. The parameter
150 is a range specified as 'start..end'. Makes sense for block group profiles that
151 utilize striping, ie. RAID0/10/5/6. The range minimum and maximum are
155 Takes no parameters. Only has meaning when converting between profiles.
156 When doing convert from one profile to another and soft mode is on,
157 chunks that already have the target profile are left untouched.
158 This is useful e.g. when half of the filesystem was converted earlier but got
161 The soft mode switch is (like every other filter) per-type.
162 For example, this means that we can convert metadata chunks the "hard" way
163 while converting data chunks selectively with soft switch.
165 Profile names, used in 'profiles' and 'convert' are one of: 'raid0', 'raid1',
166 'raid10', 'raid5', 'raid6', 'dup', 'single'. The mixed data/metadata profiles
167 can be converted in the same way, but it's conversion between mixed and non-mixed
168 is not implemented. For the constraints of the profiles please refer to `mkfs.btrfs`(8),
174 The way balance operates, it usually needs to temporarily create a new block
175 group and move the old data there. For that it needs work space, otherwise
176 it fails for ENOSPC reasons.
177 This is not the same ENOSPC as if the free space is exhausted. This refers to
178 the space on the level of block groups.
180 The free work space can be calculated from the output of the *btrfs filesystem show*
183 ------------------------------
184 Label: 'BTRFS' uuid: 8a9d72cd-ead3-469d-b371-9c7203276265
185 Total devices 2 FS bytes used 77.03GiB
186 devid 1 size 53.90GiB used 51.90GiB path /dev/sdc2
187 devid 2 size 53.90GiB used 51.90GiB path /dev/sde1
188 ------------------------------
190 'size' - 'used' = 'free work space' +
191 '53.90GiB' - '51.90GiB' = '2.00GiB'
193 An example of a filter that does not require workspace is 'usage=0'. This will
194 scan through all unused block groups of a given type and will reclaim the
195 space. After that it might be possible to run other filters.
197 **CONVERSIONS ON MULTIPLE DEVICES**
199 Conversion to profiles based on striping (RAID0, RAID5/6) require the work
200 space on each device. An interrupted balance may leave partially filled block
201 groups that might consume the work space.
205 *btrfs balance* returns a zero exit status if it succeeds. Non zero is
206 returned in case of failure.
210 *btrfs* is part of btrfs-progs.
211 Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for