1BTRFS-DEVICE(8) BTRFS BTRFS-DEVICE(8)
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6 btrfs-device - manage devices of btrfs filesystems
7
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 eg. 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 ready <device>
81 Wait until all devices of a multiple-device filesystem are
82 scanned and registered within the kernel module. This is to pro‐
83 vide a way for automatic filesystem mounting tools to wait be‐
84 fore the mount can start. The device scan is only one of the
85 preconditions and the mount can fail for other reasons. Normal
86 users usually do not need this command and may safely ignore it.
87 scan [options] [<device> [<device>...]]
89 Scan devices for a btrfs filesystem and register them with the
90 kernel module. This allows mounting multiple-device filesystem
91 by specifying just one from the whole group.
92 If no devices are passed, all block devices that blkid reports
94 to contain btrfs are scanned.
95 The options --all-devices or -d can be used as a fallback in
97 case blkid is not available. If used, behavior is the same as
98 if no devices are passed.
99 The command can be run repeatedly. Devices that have been al‐
101 ready registered remain as such. Reloading the kernel module
102 will drop this information. There's an alternative way of mount‐
103 ing multiple-device filesystem without the need for prior scan‐
104 ning. See the mount option device.
105 Options
107 -d|--all-devices
109 Enumerate and register all devices, use as a fallback in
110 case blkid is not available.
111 -u|--forget
113 Unregister a given device or all stale devices if no path
114 is given, the device must be unmounted otherwise it's an
115 error.
116 stats [options] <path>|<device>
118 Read and print the device IO error statistics for all devices of
119 the given filesystem identified by path or for a single device>.
120 The filesystem must be mounted. See section *DEVICE STATS for
121 more information about the reported statistics and the meaning.
122 Options
124 -z|--reset
126 Print the stats and reset the values to zero afterwards.
127 -c|--check
129 Check if the stats are all zeros and return 0 if it is
130 so. Set bit 6 of the return code if any of the statistics
131 is no-zero. The error values is 65 if reading stats from
132 at least one device failed, otherwise it's 64.
133 usage [options] <path> [<path>...]::
135 Show detailed information about internal allocations on devices.
136 The level of detail can differ if the command is run under a
138 regular or the root user (due to use of restricted ioctls). The
139 first example below is for normal user (warning included) and
140 the next one with root on the same filesystem:
141 WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
143 /dev/sdc1, ID: 1
144 Device size: 931.51GiB
145 Device slack: 0.00B
146 Unallocated: 931.51GiB
147 /dev/sdc1, ID: 1
149 Device size: 931.51GiB
150 Device slack: 0.00B
151 Data,single: 641.00GiB
152 Data,RAID0/3: 1.00GiB
153 Metadata,single: 19.00GiB
154 System,single: 32.00MiB
155 Unallocated: 271.48GiB
156 • Device size -- size of the device as seen by the filesystem
158 (may be different than actual device size)
159 • Device slack -- portion of device not used by the filesystem
161 but still available in the physical space provided by the de‐
162 vice, eg. after a device shrink
163 • Data,single, Metadata,single, System,single -- in general,
165 list of block group type (Data, Metadata, System) and profile
166 (single, RAID1, ...) allocated on the device
167 • Data,RAID0/3 -- in particular, striped profiles
169 RAID0/RAID10/RAID5/RAID6 with the number of devices on which
170 the stripes are allocated, multiple occurrences of the same
171 profile can appear in case a new device has been added and all
172 new available stripes have been used for writes
173 • Unallocated -- remaining space that the filesystem can still
175 use for new block groups
176 Options
178 -b|--raw
180 raw numbers in bytes, without the B suffix
181 -h|--human-readable
183 print human friendly numbers, base 1024, this is the de‐
184 fault
185 -H print human friendly numbers, base 1000
187 --iec select the 1024 base for the following options, according
189 to the IEC standard
190 --si select the 1000 base for the following options, according
192 to the SI standard
193 -k|--kbytes
195 show sizes in KiB, or kB with --si
196 -m|--mbytes
198 show sizes in MiB, or MB with --si
199 -g|--gbytes
201 show sizes in GiB, or GB with --si
202 -t|--tbytes
204 show sizes in TiB, or TB with --si
205 If conflicting options are passed, the last one takes prece‐
207 dence.
208
210 The device stats keep persistent record of several error classes re‐
211 lated to doing IO. The current values are printed at mount time and up‐
212 dated during filesystem lifetime or from a scrub run.
213 $ btrfs device stats /dev/sda3
215 [/dev/sda3].write_io_errs 0
216 [/dev/sda3].read_io_errs 0
217 [/dev/sda3].flush_io_errs 0
218 [/dev/sda3].corruption_errs 0
219 [/dev/sda3].generation_errs 0
220 write_io_errs
222 Failed writes to the block devices, means that the layers be‐
223 neath the filesystem were not able to satisfy the write request.
224 read_io_errors
226 Read request analogy to write_io_errs.
227 flush_io_errs
229 Number of failed writes with the FLUSH flag set. The flushing is
230 a method of forcing a particular order between write requests
231 and is crucial for implementing crash consistency. In case of
232 btrfs, all the metadata blocks must be permanently stored on the
233 block device before the superblock is written.
234 corruption_errs
236 A block checksum mismatched or a corrupted metadata header was
237 found.
238 generation_errs
240 The block generation does not match the expected value (eg.
241 stored in the parent node).
242 Since kernel 5.14 the device stats are also available in textual form
244 in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.
245
247 btrfs device returns a zero exit status if it succeeds. Non zero is re‐
248 turned in case of failure.
249 If the -c option is used, btrfs device stats will add 64 to the exit
251 status if any of the error counters is non-zero.
252
254 btrfs is part of btrfs-progs. Please refer to the btrfs wiki
255 http://btrfs.wiki.kernel.org for further details.
256
258 mkfs.btrfs(8), btrfs-replace(8), btrfs-balance(8)
259
261 2022
2625.18 May 25, 2022 BTRFS-DEVICE(8)