1BTRFS-DEVICE(8) BTRFS BTRFS-DEVICE(8)
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6 btrfs-device - manage devices of btrfs filesystems
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9 btrfs device <subcommand> <args>
10
12 The btrfs device command group is used to manage devices of the btrfs
13 filesystems.
14
17 add [-Kf] <device> [<device>...] <path>
18 Add device(s) to the filesystem identified by path.
19 If applicable, a whole device discard (TRIM) operation is per‐
21 formed prior to adding the device. A device with existing
22 filesystem detected by blkid(8) will prevent device addition and
23 has to be forced. Alternatively the filesystem can be wiped from
24 the device using e.g. the wipefs(8) tool.
25 The operation is instant and does not affect existing data. The
27 operation merely adds the device to the filesystem structures
28 and creates some block groups headers.
29 Options
31 -K|--nodiscard
33 do not perform discard (TRIM) by default
34 -f|--force
36 force overwrite of existing filesystem on the given
37 disk(s)
38 --enqueue
40 wait if there's another exclusive operation running, oth‐
41 erwise continue
42 remove [options] <device>|<devid> [<device>|<devid>...] <path>
44 Remove device(s) from a filesystem identified by <path>
45 Device removal must satisfy the profile constraints, otherwise
47 the command fails. The filesystem must be converted to pro‐
48 file(s) that would allow the removal. This can typically happen
49 when going down from 2 devices to 1 and using the RAID1 profile.
50 See the section TYPICAL USECASES.
51 The operation can take long as it needs to move all data from
53 the device.
54 It is possible to delete the device that was used to mount the
56 filesystem. The device entry in the mount table will be replaced
57 by another device name with the lowest device id.
58 If the filesystem is mounted in degraded mode (-o degraded),
60 special term missing can be used for device. In that case, the
61 first device that is described by the filesystem metadata, but
62 not present at the mount time will be removed.
63 NOTE:
65 In most cases, there is only one missing device in degraded
66 mode, otherwise mount fails. If there are two or more devices
67 missing (e.g. possible in RAID6), you need specify missing as
68 many times as the number of missing devices to remove all of
69 them.
70 Options
72 --enqueue
74 wait if there's another exclusive operation running, oth‐
75 erwise continue
76 delete <device>|<devid> [<device>|<devid>...] <path>
78 Alias of remove kept for backward compatibility
79 replace <command> [options] <path>
81 Alias of whole command group btrfs replace for convenience. See
82 btrfs-replace(8).
83 ready <device>
85 Wait until all devices of a multiple-device filesystem are
86 scanned and registered within the kernel module. This is to pro‐
87 vide a way for automatic filesystem mounting tools to wait be‐
88 fore the mount can start. The device scan is only one of the
89 preconditions and the mount can fail for other reasons. Normal
90 users usually do not need this command and may safely ignore it.
91 scan [options] [<device> [<device>...]]
93 Scan devices for a btrfs filesystem and register them with the
94 kernel module. This allows mounting multiple-device filesystem
95 by specifying just one from the whole group.
96 If no devices are passed, all block devices that blkid reports
98 to contain btrfs are scanned.
99 The options --all-devices or -d can be used as a fallback in
101 case blkid is not available. If used, behavior is the same as
102 if no devices are passed.
103 The command can be run repeatedly. Devices that have been al‐
105 ready registered remain as such. Reloading the kernel module
106 will drop this information. There's an alternative way of mount‐
107 ing multiple-device filesystem without the need for prior scan‐
108 ning. See the mount option device.
109 Options
111 -d|--all-devices
113 Enumerate and register all devices, use as a fallback in
114 case blkid is not available.
115 -u|--forget
117 Unregister a given device or all stale devices if no path
118 is given, the device must be unmounted otherwise it's an
119 error.
120 stats [options] <path>|<device>
122 Read and print the device IO error statistics for all devices of
123 the given filesystem identified by path or for a single device>.
124 The filesystem must be mounted. See section *DEVICE STATS for
125 more information about the reported statistics and the meaning.
126 Options
128 -z|--reset
130 Print the stats and reset the values to zero afterwards.
131 -c|--check
133 Check if the stats are all zeros and return 0 if it is
134 so. Set bit 6 of the return code if any of the statistics
135 is no-zero. The error values is 65 if reading stats from
136 at least one device failed, otherwise it's 64.
137 -T Print stats in a tabular form, devices as rows and stats
139 as columns
140 usage [options] <path> [<path>...]::
142 Show detailed information about internal allocations on devices.
143 The level of detail can differ if the command is run under a
145 regular or the root user (due to use of restricted ioctls). The
146 first example below is for normal user (warning included) and
147 the next one with root on the same filesystem:
148 WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
150 /dev/sdc1, ID: 1
151 Device size: 931.51GiB
152 Device slack: 0.00B
153 Unallocated: 931.51GiB
154 /dev/sdc1, ID: 1
156 Device size: 931.51GiB
157 Device slack: 0.00B
158 Data,single: 641.00GiB
159 Data,RAID0/3: 1.00GiB
160 Metadata,single: 19.00GiB
161 System,single: 32.00MiB
162 Unallocated: 271.48GiB
163 • Device size -- size of the device as seen by the filesystem
165 (may be different than actual device size)
166 • Device slack -- portion of device not used by the filesystem
168 but still available in the physical space provided by the de‐
169 vice, e.g. after a device shrink
170 • Data,single, Metadata,single, System,single -- in general,
172 list of block group type (Data, Metadata, System) and profile
173 (single, RAID1, ...) allocated on the device
174 • Data,RAID0/3 -- in particular, striped profiles
176 RAID0/RAID10/RAID5/RAID6 with the number of devices on which
177 the stripes are allocated, multiple occurrences of the same
178 profile can appear in case a new device has been added and all
179 new available stripes have been used for writes
180 • Unallocated -- remaining space that the filesystem can still
182 use for new block groups
183 Options
185 -b|--raw
187 raw numbers in bytes, without the B suffix
188 -h|--human-readable
190 print human friendly numbers, base 1024, this is the de‐
191 fault
192 -H print human friendly numbers, base 1000
194 --iec select the 1024 base for the following options, according
196 to the IEC standard
197 --si select the 1000 base for the following options, according
199 to the SI standard
200 -k|--kbytes
202 show sizes in KiB, or kB with --si
203 -m|--mbytes
205 show sizes in MiB, or MB with --si
206 -g|--gbytes
208 show sizes in GiB, or GB with --si
209 -t|--tbytes
211 show sizes in TiB, or TB with --si
212 If conflicting options are passed, the last one takes prece‐
214 dence.
215
217 The device stats keep persistent record of several error classes re‐
218 lated to doing IO. The current values are printed at mount time and up‐
219 dated during filesystem lifetime or from a scrub run.
220 $ btrfs device stats /dev/sda3
222 [/dev/sda3].write_io_errs 0
223 [/dev/sda3].read_io_errs 0
224 [/dev/sda3].flush_io_errs 0
225 [/dev/sda3].corruption_errs 0
226 [/dev/sda3].generation_errs 0
227 write_io_errs
229 Failed writes to the block devices, means that the layers be‐
230 neath the filesystem were not able to satisfy the write request.
231 read_io_errors
233 Read request analogy to write_io_errs.
234 flush_io_errs
236 Number of failed writes with the FLUSH flag set. The flushing is
237 a method of forcing a particular order between write requests
238 and is crucial for implementing crash consistency. In case of
239 btrfs, all the metadata blocks must be permanently stored on the
240 block device before the superblock is written.
241 corruption_errs
243 A block checksum mismatched or a corrupted metadata header was
244 found.
245 generation_errs
247 The block generation does not match the expected value (e.g.
248 stored in the parent node).
249 Since kernel 5.14 the device stats are also available in textual form
251 in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.
252
254 btrfs device returns a zero exit status if it succeeds. Non zero is re‐
255 turned in case of failure.
256 If the -c option is used, btrfs device stats will add 64 to the exit
258 status if any of the error counters is non-zero.
259
261 btrfs is part of btrfs-progs. Please refer to the documentation at
262 https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for
263 further information.
264
266 btrfs-balance(8) btrfs-device(8), btrfs-replace(8), mkfs.btrfs(8),
2676.1.3 Jan 25, 2023 BTRFS-DEVICE(8)