1.\" Copyright (c) 2007 Matthew Jacob 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd March 17, 2022 26.Dt GMULTIPATH 8 27.Os 28.Sh NAME 29.Nm gmultipath 30.Nd "disk multipath control utility" 31.Sh SYNOPSIS 32.Nm 33.Cm create 34.Op Fl ARv 35.Ar name 36.Ar prov ... 37.Nm 38.Cm label 39.Op Fl ARv 40.Ar name 41.Ar prov ... 42.Nm 43.Cm configure 44.Op Fl APRv 45.Ar name 46.Nm 47.Cm add 48.Op Fl v 49.Ar name prov 50.Nm 51.Cm remove 52.Op Fl v 53.Ar name prov 54.Nm 55.Cm fail 56.Op Fl v 57.Ar name prov 58.Nm 59.Cm restore 60.Op Fl v 61.Ar name prov 62.Nm 63.Cm rotate 64.Op Fl v 65.Ar name 66.Nm 67.Cm prefer 68.Op Fl v 69.Ar name 70.Ar prov 71.Nm 72.Cm getactive 73.Op Fl v 74.Ar name 75.Nm 76.Cm destroy 77.Op Fl v 78.Ar name 79.Nm 80.Cm stop 81.Op Fl v 82.Ar name 83.Nm 84.Cm clear 85.Op Fl v 86.Ar prov ... 87.Nm 88.Cm list 89.Nm 90.Cm status 91.Nm 92.Cm load 93.Nm 94.Cm unload 95.Sh DESCRIPTION 96The 97.Nm 98utility is used for device multipath configuration. 99.Pp 100The multipath device can be configured using two different methods: 101.Dq manual 102or 103.Dq automatic . 104When using the 105.Dq manual 106method, no metadata are stored on the devices, so the multipath 107device has to be configured by hand every time it is needed. 108Additional device paths also will not be detected automatically. 109The 110.Dq automatic 111method uses on-disk metadata to detect device and all its paths. 112Metadata use the last sector of the underlying disk device and 113include device name and UUID. 114The UUID guarantees uniqueness in a shared storage environment 115but is in general too cumbersome to use. 116The name is what is exported via the device interface. 117.Pp 118The first argument to 119.Nm 120indicates an action to be performed: 121.Bl -tag -width ".Cm destroy" 122.It Cm create 123Create multipath device with 124.Dq manual 125method without writing any on-disk metadata. 126It is up to administrator, how to properly identify device paths. 127Kernel will only check that all given providers have same media and 128sector sizes. 129.Pp 130.Fl A 131option enables Active/Active mode, 132.Fl R 133option enables Active/Read mode, otherwise Active/Passive mode is used 134by default. 135.It Cm label 136Create multipath device with 137.Dq automatic 138method. 139Label the first given provider with on-disk metadata using the specified 140.Ar name . 141The rest of given providers will be retasted to detect these metadata. 142It reliably protects against specifying unrelated providers. 143Providers with no matching metadata detected will not be added to the device. 144.Pp 145.Fl A 146option enables Active/Active mode, 147.Fl R 148option enables Active/Read mode, otherwise Active/Passive mode is used 149by default. 150.It Cm configure 151Configure the given multipath device. 152.Pp 153.Fl A 154option enables Active/Active mode, 155.Fl P 156option enables Active/Passive mode, 157.Fl R 158option enables Active/Read mode. 159.It Cm add 160Add the given provider as a path to the given multipath device. 161Should normally be used only for devices created with 162.Dq manual 163method, unless you know what you are doing (you are sure that it is another 164device path, but tasting its metadata in regular 165.Dq automatic 166way is not possible). 167.It Cm remove 168Remove the given provider as a path from the given multipath device. 169If the last path removed, the multipath device will be destroyed. 170.It Cm fail 171Mark specified provider as a path of the specified multipath device as failed. 172If there are other paths present, new requests will be forwarded there. 173.It Cm restore 174Mark specified provider as a path of the specified multipath device as 175operational, allowing it to handle requests. 176.It Cm rotate 177Change the active provider/path to the next available provider in Active/Passive mode. 178.It Cm prefer 179Change the active provider/path to the specified provider in Active/Passive mode. 180.It Cm getactive 181Get the currently active provider(s)/path(s). 182.It Cm destroy 183Destroy the given multipath device clearing metadata. 184.It Cm stop 185Stop the given multipath device without clearing metadata. 186.It Cm clear 187Clear metadata on the given provider. 188.It Cm list 189See 190.Xr geom 8 . 191.It Cm status 192See 193.Xr geom 8 . 194.It Cm load 195See 196.Xr geom 8 . 197.It Cm unload 198See 199.Xr geom 8 . 200.El 201.Sh SYSCTL VARIABLES 202The following 203.Xr sysctl 8 204variable can be used to control the behavior of the 205.Nm MULTIPATH 206GEOM class. 207.Bl -tag -width indent 208.It Va kern.geom.multipath.debug : No 0 209Debug level of the 210.Nm MULTIPATH 211GEOM class. 212This can be set to 0 (default) or 1 to disable or enable various 213forms of chattiness. 214.It Va kern.geom.multipath.exclusive : No 1 215Open underlying providers exclusively, preventing individual paths access. 216.El 217.Sh EXIT STATUS 218Exit status is 0 on success, and 1 if the command fails. 219.Sh MULTIPATH ARCHITECTURE 220This is a multiple path architecture with no device knowledge or 221presumptions other than size matching built in. 222Therefore the user must exercise some care 223in selecting providers that do indeed represent multiple paths to the 224same underlying disk device. 225The reason for this is that there are several 226criteria across multiple underlying transport types that can 227.Ar indicate 228identity, but in all respects such identity can rarely be considered 229.Ar definitive . 230.Pp 231For example, if you use the World Wide Port Name of a Fibre Channel 232disk object you might believe that two disks that have the same WWPN 233on different paths (or even disjoint fabrics) might be considered 234the same disk. 235Nearly always this would be a safe assumption, until 236you realize that a WWPN, like an Ethernet MAC address, is a soft 237programmable entity, and that a misconfigured Director Class switch 238could lead you to believe incorrectly that you have found multiple 239paths to the same device. 240This is an extreme and theoretical case, but 241it is possible enough to indicate that the policy for deciding which 242of multiple pathnames refer to the same device should be left to the 243system operator who will use tools and knowledge of their own storage 244subsystem to make the correct configuration selection. 245.Pp 246There are Active/Passive, Active/Read and Active/Active operation modes 247supported. 248In Active/Passive mode only one path has I/O moving on it 249at any point in time. 250This I/O continues until an I/O is returned with 251a generic I/O error or a "Nonexistent Device" error. 252When this occurs, that path is marked FAIL, the next path 253in a list is selected as active and the failed I/O reissued. 254In Active/Active mode all paths not marked FAIL may handle I/O at the same time. 255Requests are distributed between paths to equalize load. 256For capable devices it allows the utilisation of the bandwidth available on all paths. 257In Active/Read mode all paths not marked FAIL may handle reads at the same time, 258but unlike in Active/Active mode only one path handles write requests at any 259point in time; closely following the original write request order if the layer 260above needs it for data consistency (not waiting for requisite write completion 261before sending dependent write). 262.Pp 263When new devices are added to the system the 264.Nm MULTIPATH 265GEOM class is given an opportunity to taste these new devices. 266If a new 267device has a 268.Nm MULTIPATH 269on-disk metadata label, the device is either used to create a new 270.Nm MULTIPATH 271GEOM, or added to the list of paths for an existing 272.Nm MULTIPATH 273GEOM. 274.Pp 275It is this mechanism that works reasonably with 276.Xr isp 4 277and 278.Xr mpt 4 279based Fibre Channel disk devices. 280For these devices, when a device disappears 281(due to e.g., a cable pull or power failure to a switch), the device is 282proactively marked as gone and I/O to it failed. 283This causes the 284.Nm MULTIPATH 285failure event just described. 286.Pp 287When Fibre Channel events inform either 288.Xr isp 4 289or 290.Xr mpt 4 291host bus adapters that new devices may have arrived (e.g., the arrival 292of an RSCN event from the Fabric Domain Controller), they can cause 293a rescan to occur and cause the attachment and configuration of any 294(now) new devices to occur, causing the taste event described above. 295.Pp 296This means that this multipath architecture is not a one-shot path 297failover, but can be considered to be steady state as long as failed 298paths are repaired (automatically or otherwise). 299.Pp 300Automatic rescanning is not a requirement. 301Nor is Fibre Channel. 302The 303same failover mechanisms work equally well for traditional "Parallel" 304SCSI but may require manual intervention with 305.Xr camcontrol 8 306to cause the reattachment of repaired device links. 307.Sh EXAMPLES 308The following example shows how to use 309.Xr camcontrol 8 310to find possible multiple path devices and to create a 311.Nm MULTIPATH 312GEOM class for them. 313.Bd -literal -offset indent 314mysys# camcontrol devlist 315<ECNCTX @WESTVILLE > at scbus0 target 0 lun 0 (da0,pass0) 316<ECNCTX @WESTVILLE > at scbus0 target 0 lun 1 (da1,pass1) 317<ECNCTX @WESTVILLE > at scbus1 target 0 lun 0 (da2,pass2) 318<ECNCTX @WESTVILLE > at scbus1 target 0 lun 1 (da3,pass3) 319mysys# camcontrol inquiry da0 -S 320ECNTX0LUN000000SER10ac0d01 321mysys# camcontrol inquiry da2 -S 322ECNTX0LUN000000SER10ac0d01 323.Ed 324.Pp 325Now that you have used the Serial Number to compare two disk paths 326it is not entirely unreasonable to conclude that these are multiple 327paths to the same device. 328However, only the user who is familiar 329with their storage is qualified to make this judgement. 330.Pp 331You can then use the 332.Nm 333command to label and create a 334.Nm MULTIPATH 335GEOM provider named 336.Ar FRED . 337.Bd -literal -offset indent 338gmultipath label -v FRED /dev/da0 /dev/da2 339disklabel -Bw /dev/multipath/FRED auto 340newfs /dev/multipath/FREDa 341mount /dev/multipath/FREDa /mnt.... 342.Ed 343.Pp 344The resultant console output looks something like: 345.Bd -literal -offset indent 346GEOM_MULTIPATH: da0 added to FRED 347GEOM_MULTIPATH: da0 is now active path in FRED 348GEOM_MULTIPATH: da2 added to FRED 349.Ed 350.Pp 351To load the 352.Nm 353module at boot time, add this entry to 354.Pa /boot/loader.conf : 355.Bd -literal -offset ident 356geom_multipath_load="YES" 357.Ed 358.Sh SEE ALSO 359.Xr geom 4 , 360.Xr isp 4 , 361.Xr mpt 4 , 362.Xr loader.conf 5 , 363.Xr camcontrol 8 , 364.Xr geom 8 , 365.Xr mount 8 , 366.Xr newfs 8 , 367.Xr sysctl 8 368.Sh HISTORY 369The 370.Nm 371utility first appeared in 372.Fx 7.0 373.Sh AUTHORS 374.An Matthew Jacob Aq Mt mjacob@FreeBSD.org 375.An Alexander Motin Aq Mt mav@FreeBSD.org 376