diff options
Diffstat (limited to 'mdadm.8')
| -rw-r--r-- | mdadm.8 | 170 |
1 files changed, 164 insertions, 6 deletions
@@ -1,5 +1,5 @@ .\" -*- nroff -*- -.TH MDADM 8 "" v1.5.0 +.TH MDADM 8 "" v1.6.0 .SH NAME mdadm \- manage MD devices .I aka @@ -76,7 +76,7 @@ configuration file, at all. It has a different configuration file with a different format and an different purpose. .SH MODES -mdadm has 6 major modes of operation: +mdadm has 7 major modes of operation: .TP .B Assemble Assemble the parts of a previously created @@ -114,6 +114,12 @@ only meaningful for raid1, 4, 5, 6 or multipath arrays as only these have interesting state. raid0 or linear never have missing, spare, or failed drives, so there is nothing to monitor. +.TP +.B "Grow" +Grow (or shrink) an array, or otherwise reshape it in some way. +Currently supported growth options including changing the active size +of componenet devices in RAID level 1/4/5/6 and changing the number of +active devices in RAID1. .SH OPTIONS @@ -153,6 +159,10 @@ Select mode. .TP +.BR -G ", " --grow +Change the size or shape of an active array. + +.TP .BR -h ", " --help Display help message or, after above option, mode specific help message. @@ -261,13 +271,17 @@ Specify the number of active devices in the array. This, plus the number of spare devices (see below) must equal the number of .I component-devices (including "\fBmissing\fP" devices) -that are listed on the command line. Setting a value of 1 is probably +that are listed on the command line for +.BR --create . +Setting a value of 1 is probably a mistake and so requires that .B --force be specified first. A value of 1 will then be allowed for linear, multipath, raid0 and raid1. It is never allowed for raid4 or raid5. .br -Note that this number cannot be changed once the array has been created. +This number can only be changed using +.B --grow +for RAID1 arrays, and only on kernels which provide necessary support. .TP .BR -x ", " --spare-devices= @@ -288,6 +302,63 @@ If this is not specified size, though if there is a variance among the drives of greater than 1%, a warning is issued. +This value can be set with +.B --grow +for RAID level 1/4/5/6. If the array was created with a size smaller +than the currently active drives, the extra space can be accessed +using +.BR --grow . + +.TP +.BR --assume-clean +Tell +.I mdadm +that the array pre-existed and is known to be clean. This is only +really useful for Building RAID1 array. Only use this if you really +know what you are doing. This is currently only supported for --build. + +.TP +.BR -R ", " --run +Insist that +.I mdadm +run the array, even if some of the components +appear to be active in another array or filesystem. Normally +.I mdadm +will ask for confirmation before including such components in an +array. This option causes that question to be suppressed. + +.TP +.BR -f ", " --force +Insist that +.I mdadm +accept the geometry and layout specified without question. Normally +.I mdadm +will not allow creation of an array with only one device, and will try +to create a raid5 array with one missing drive (as this makes the +initial resync work faster). With +.BR --force , +.I mdadm +will not try to be so clever. + +.TP +.BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}" +Instruct mdadm to create the device file if needed, and to allocate +an unused minor number. "yes" or "md" causes a non-partitionable array +to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and +later) to be used. The argumentment can also come immediately after +"-a". e.g. "-ap". + +For partitionable arrays, +.I mdadm +will create the device file for the whole array and for the first 4 +partitions. A different number of partitions can be specified at the +end of this option (e.g. +.BR --auto=p7 ). +If the device name ends with a digit, the partition names add an +underscore, a 'p', and a number, e.g. "/dev/home1_p3". If there is no +trailing digit, then the partition names just have a number added, +e.g. "/dev/scratch3". + .SH For assemble: .TP @@ -327,6 +398,10 @@ With an attempt will be made to start it anyway. .TP +.BR -a ", " "--auto{=no,yes,md,mdp,part}" +See this option under Create and Build options. + +.TP .BR -U ", " --update= Update the superblock on each device while assembling the array. The argument given to this flag can be one of @@ -504,7 +579,7 @@ listed in the configuration file are assembled. If precisely one device is listed, but .B --scan -is not given, that +is not given, then .I mdadm acts as though .B --scan @@ -545,6 +620,46 @@ may work for RAID1, 4, 5 or 6), give the .B --run flag. +If an +.B auto +option is given, either on the command line (--auto) or in the +configuration file (e.g. auto=part), then +.I mdadm +will create the md device if necessary or will re-create it if it +doesn't look usable as it is. + +This can be useful for handling partitioned devices (which don't have +a stable device number - it can change after a reboot) and when using +"udev" to manage your +.B /dev +tree (udev cannot handle md devices because of the unusual device +initialisation conventions). + +If the option to "auto" is "mdp" or "part" or (on the command line +only) "p", then mdadm will create a partitionable array, using the +first free one that is not inuse, and does not already have an entry +in /dev (apart from numeric /dev/md* entries). + +If the option to "auto" is "yes" or "md" or (on the command line) +nothing, then mdadm will create a traditional, non-partitionable md +array. + +It is expected that the "auto" functionality will be used to create +device entries with meaningful names such as "/dev/md/home" or +"/dev/md/root", rather than names based on the numerical array number. + +When using this option to create a partitionable array, the device +files for the first 4 partitions are also created. If a different +number is required it can be simply appended to the auto option. +e.g. "auto=part8". Partition names are created by appending a digit +string to the device name, with an intervening "_p" if the device name +ends with a digit. + +The +.B --auto +option is also available in Build and Create modes. As those modes do +not use a config file, the "auto=" config option does not apply to +these modes. .SH BUILD MODE @@ -584,6 +699,12 @@ Usage: This usage will initialise a new md array, associate some devices with it, and activate the array. +This the +.B --auto +option is given (as described in more detail in the section on +Assemble mode), then the md device will be created with a suitable +device number if necessary. + As devices are added, they are checked to see if they contain raid superblocks or filesystems. They are also checked to see if the variance in device size exceeds 1%. @@ -625,7 +746,7 @@ option. The General Management options that are valid with --create are: .TP .B --run -insist of running the array even if some devices look like they might +insist on running the array even if some devices look like they might be in use. .TP @@ -921,6 +1042,43 @@ first. If the removal succeeds but the adding fails, then it is added back to the original array. +.SH GROW MODE +The GROW mode is used for changing the size or shape of an active +array. +For this to work, the kernel must support the necessary change. +Various types of growth may be added during 2.6 development, possibly +including restructuring a raid5 array to have more active devices. + +Currently the only support available is to change the "size" attribute +for arrays with redundancy, and the raid-disks attribute of RAID1 +arrays. + +Normally when an array is build the "size" it taken from the smallest +of the drives. If all the small drives in an arrays are, one at a +time, removed and replaced with larger drives, then you could have an +array of large drives with only a small amount used. In this +situation, changing the "size" with "GROW" mode will allow the extra +space to start being used. If the size is increased in this way, a +"resync" process will start to make sure the new parts of the array +are synchronised. + +Note that when an array changes size, any filesystem that may be +stored in the array will not automatically grow to use the space. The +filesystem will need to be explicitly told to use the extra space. + +A RAID1 array can work with any number of devices from 1 upwards +(though 1 is not very useful). There may be times which you want to +increase or decrease the number of active devices. Note that this is +different to hot-add or hot-remove which changes the number of +inactive devices. + +When reducing the number of devices in a RAID1 array, the slots which +are to be removed from the array must already be vacant. That is, the +devices that which were in those slots must be failed and removed. + +When the number of devices is increased, any hot spares that are +present may be activated immediately. + .SH EXAMPLES .B " mdadm --query /dev/name-of-device" |