mdadm(8) mdadm(8) NNAAMMEE mdadm - manage MD devices _a_k_a Linux Software Raid. SSYYNNOOPPSSIISS mmddaaddmm _[_m_o_d_e_] _<_r_a_i_d_d_e_v_i_c_e_> _[_o_p_t_i_o_n_s_] _<_s_u_b_d_e_v_i_c_e_s_> DDEESSCCRRIIPPTTIIOONN RAID devices are virtual devices created from two or more real block devices. This allows multiple devices (typi- cally disk drives or partitions there-of) to be combined into a single device to hold (for example) a single filesystem. Some RAID levels included redundancy and so can survive some degree of device failure. Linux Software RAID devices are implemented through the md (Multiple Devices) device driver. Currently, Linux supports LLIINNEEAARR md devices, RRAAIIDD00 (strip- ing), RRAAIIDD11 (mirroring), RRAAIIDD44 and RRAAIIDD55.. Recent kernels (2002) also support a mode known as MMUULLTTII-- PPAATTHH. mmddaaddmm does not support MULTIPATH as yet. mmddaaddmm is a program that can be used to create, manage, and monitor MD devices. As such it provides a similar set of functionality to the rraaiiddttoooollss packages. The key differ- ences between mmddaaddmm and rraaiiddttoooollss are: +o mmddaaddmm is a single program and not a collection of pro- grams. +o mmddaaddmm can perform (almost) all of its functions with- out having a configuration file. Also mdadm helps with management of the configuration file. +o mmddaaddmm can provide information about your arrays (through Detail and Examine) that rraaiiddttoooollss cannot. +o rraaiiddttoooollss can manage MULTIPATH devices which mmddaaddmm cannot yet manage. MMOODDEESS mdadm has 7 major modes of operation: AAsssseemmbbllee Assemble the parts of a previously created array into an active array. Components can be explicitly given or can be searched for. mmddaaddmm checks that the components do form a bona fide array, and can, on request, fiddle superblock information so as to assemble a faulty array. BBuuiilldd Build a legacy array without per-device superblocks. CCrreeaattee Create a new array with per-device superblocks. DDeettaaiill Display the details of a given md device. Details include the RAID level, the number of devices, which ones are faulty (if any), and the array UUID. EExxaammiinnee Examine a device to see if it is part of an md array, and print out the details of that array. This mode can also be used to examine a large num- ber of devices and to print out a summary of the arrays found in a format suitable for the mmddaaddmm..ccoonnff configuration file. FFoollllooww oorr MMoonniittoorr Monitor one or more md devices and act on any state changes. MMaannaaggee This is for odd bits an pieces like hotadd, hotremove, setfaulty, stop, readonly, readwrite. OOPPTTIIOONNSS Available options are: --AA, ----aasssseemmbbllee Assemble an existing array. --BB, ----bbuuiilldd Build a legacy array without superblocks. --CC, ----ccrreeaattee Create a new array. --DD, ----ddeettaaiill Print detail of one or more md devices. --EE, ----eexxaammiinnee Print content of md superblock on device(s). --FF, ----ffoollllooww, ----mmoonniittoorr Select MMoonniittoorr mode. --hh, ----hheellpp Display help message or, after above option, mode specific help message. --VV, ----vveerrssiioonn Print version information for mdadm. --vv, ----vveerrbboossee Be more verbose about what is happening. --bb, ----bbrriieeff Be less verbose. This is used with ----ddeettaaiill and ----eexxaammiinnee. FFoorr ccrreeaattee oorr bbuuiilldd:: --cc, ----cchhuunnkk== Specify chunk size of kibibytes. The default is 64. ----rroouunnddiinngg== Specify rounding factor for linear array (==chunk size) --ll, ----lleevveell== Set raid level. Options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid5, 4, raid5, 5. Obviously some of these are synonymous. Only the first 4 are valid when Building. --pp, ----ppaarriittyy== Set raid5 parity algorithm. Options are: {left,right}-{,a}symmetric, la, ra, ls, rs. The default is left-symmetric. ----llaayyoouutt== same as --parity --nn, ----rraaiidd--ddiisskkss== number of active devices in array. --xx, ----ssppaarree--ddiisskkss== number of spare (eXtra) disks in initial array. Spares can be added and removed later. --zz, ----ssiizzee== Amount (in Kibibytes) of space to use from each drive in RAID1/4/5. This must be a multiple of the chunk size, and must leave about 128Kb of space at the end of the drive for the RAID superblock. If this is not specified (as it normally is not) the smallest drive (or partition) sets the size, though if there is a variance among the drives of greater than 1%, a warning is issued. FFoorr aasssseemmbbllee:: --uu, ----uuuuiidd== uuid of array to assemble. Devices which don't have this uuid are excluded --mm, ----ssuuppeerr--mmiinnoorr== Minor number of device that array was created for. Devices which don't have this minor number are excluded. If you create an array as /dev/md1, then all superblock will contain the minor number 1, even if the array is later assembled as /dev/md2. --cc, ----ccoonnffiigg== config file. Default is //eettcc//mmddaaddmm..ccoonnff. --ss, ----ssccaann scan config file for missing information --ff, ----ffoorrccee Assemble the array even if some superblocks appear out-of-date --RR, ----rruunn Attempt to start the array even if fewer drives were given than are needed for a full array. Nor- mally if not all drives are found and ----ssccaann is not used, then the array will be assembled but not started. With ----rruunn an attempt will be made to start it anyway. GGeenneerraall mmaannaaggeemmeenntt --aa, ----aadddd hotadd listed devices. --rr, ----rreemmoovvee remove listed devices. The must not be active. i.e. they should be failed or spare devices. --ff, ----ffaaiill mark listed devices as faulty. ----sseett--ffaauullttyy same as --fail. --RR, ----rruunn start a partially built array. --SS, ----ssttoopp deactivate array, releasing all resources. --oo, ----rreeaaddoonnllyy mark array as readonly. --ww, ----rreeaaddwwrriittee mark array as readwrite. AASSSSEEMMBBLLYY MMOODDEE Usage: mmddaaddmm ----aasssseemmbbllee _d_e_v_i_c_e _o_p_t_i_o_n_s_._._. Usage: mmddaaddmm ----aasssseemmbbllee ----ssccaann _o_p_t_i_o_n_s_._._. This usage assembles one or more raid arrays from pre- existing components. For each array, mdadm needs to know the md device, the identity of the array, and a number of sub devices. These can be found in a number of ways. The md device is either given before ----ssccaann or is found from the config file. In the latter case, multiple md devices can be started with a single mdadm command. The identity can be given with the ----uuuuiidd option, with the ----ssuuppeerr--mmiinnoorr option, can be found in in the config file, or will be taken from the super block on the first subde- vice listed on the command line. Devices can be given on the ----aasssseemmbbllee command line or from the config file. Only devices which have an md superblock which contains the right identity will be con- sidered for any device. The config file is only used if explicitly named with ----ccoonnffiigg or requested with ----ssccaann.. In the later case, //eettcc//mmddaaddmm..ccoonnff is used. If ----ssccaann is not given, then the config file will only be used to find the identity of md arrays. Normally the array will be started after it is assembled. However is ----ssccaann is not given and insufficient drives were lists to start a complete (non-degraded) array, then the array is not started (to guard against usage errors). To insist that the array be started in this case (as may work for RAID1 or RAID5), give the ----rruunn flag. BBUUIILLDD MMOODDEE Usage: mmddaaddmm ----bbuuiilldd _d_e_v_i_c_e ----cchhuunnkk==_X ----lleevveell==_Y ----rraaiidd-- ddiisskkss==_Z _d_e_v_i_c_e_s This usage is similar to ----ccrreeaattee. The difference is that it creates a legacy array without a superblock. With these arrays there is no difference between initially creating the array and subsequently assembling the array, except that hopefully there is useful data there in the second case. The level may only be 0, raid0, or linear. All devices must be listed and the array will be started once com- plete. CCRREEAATTEE MMOODDEE Usage: mmddaaddmm ----ccrreeaattee _d_e_v_i_c_e ----cchhuunnkk==_X ----lleevveell==_Y ----rraaiidd--ddiisskkss==_Z _d_e_v_i_c_e_s This usage will initialise a new md array, associate some devices with it, and activate the array. As devices are added, they are checked to see if they con- tain raid superblocks or filesystems. They are also check to see if the variance in device size exceeds 1%. If any discrepancy is found, the array will not automati- cally be run, though the presence of a ----rruunn can override this caution. The General Management options that are valid with --cre- ate are: ----rruunn insist of running the array even if some devices look like they might be in use. ----rreeaaddoonnllyy start the array readonly - not supported yet. DDEETTAAIILL MMOODDEE Usage: mmddaaddmm ----ddeettaaiill [----bbrriieeff] _d_e_v_i_c_e _._._. This usage sill print out the details of the given array including a list of component devices. To determine names for the devices, mmddaaddmm searches //ddeevv for device files with the right major and minor numbers. With ----bbrriieeff mmddaaddmm prints a single line that identifies the level, number of disks, and UUID of the array. This line is suitable for inclusion in //eettcc//mmddaaddmm..ccoonnff. EEXXAAMMIINNEE MMOODDEE Usage: mmddaaddmm ----eexxaammiinnee [----ssccaann] [----bbrriieeff] _d_e_v_i_c_e _._._. This usage will examine some block devices to see if that have a valid RAID superblock on them. The information in each valid raid superblock will be printed. If ----ssccaann is used, the no devices should be listed, and the complete set of devices identified in the configura- tion file are checked. ----ssccaann implies ----bbrriieeff but this implication can be countered by specifying ----vveerrbboossee. With ----bbrriieeff mmddaaddmm will output an config file entry of each distinct array that was found. This entry will list the UUID, the raid level, and a list of the individual devices on which a superblock for that array was found. This output will by syntactically suitable for inclusion in the configuration file, but should NNOOTT be used blindly. Often the array description that you want in the configu- ration file is much less specific than that given by mmddaaddmm --BBss. For example, you normally do not want to list the devices, particularly if they are SCSI devices. FFIILLEESS //pprroocc//mmddssttaatt If you're using the //pprroocc filesystem, //pprroocc//mmddssttaatt gives you informations about md devices status. This file is not currently used by mmddaaddmm. //eettcc//mmddaaddmm..ccoonnff The config file lists which devices may be scanned to see if they contain MD super block, and gives identifying information (e.g. UUID) about known MD arrays. See mmddaaddmm..ccoonnff(5) for more details. TTOODDOO Finish and document Follow mode. SSEEEE AALLSSOO For information on the various levels of RAID, check out: http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/ for new releases of the RAID driver check out: ftp://ftp.kernel.org/pub/linux/kernel/peo- ple/mingo/raid-patches or http://www.cse.unsw.edu.au/~neilb/patches/linux- stable/ mmddaaddmm..ccoonnff(5), mmdd(4). _r_a_i_d_t_a_b(5), _r_a_i_d_0_r_u_n(8), _r_a_i_d_s_t_o_p(8), _m_k_r_a_i_d(8) mdadm(8)