mdadm-0.7.1
[thirdparty/mdadm.git] / md.man
1 MD(4) MD(4)
2
3
4
5 N\bNA\bAM\bME\bE
6 md - Multiple Device driver aka Linux Software Raid
7
8 S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
9 /\b/d\bde\bev\bv/\b/m\bmd\bd_\bn
10 /\b/d\bde\bev\bv/\b/m\bmd\bd/\b/_\bn
11
12 D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
13 The m\bmd\bd driver provides virtual devices that are created
14 from one or more independant underlying devices. This
15 array of devices often contains redundancy, and hence the
16 acronym RAID which stands for a Redundant Array of Inde-
17 pendant Devices.
18
19 m\bmd\bd support RAID levels 1 (mirroring) 4 (striped array with
20 parity device) and 5 (striped array with distributed par-
21 ity information. If a single underlying device fails
22 while using one of these level, they array will continue
23 to function.
24
25 m\bmd\bd also supports a number of pseudo RAID (non-redundant)
26 configuations including RAID0 (striped array), LINEAR
27 (catenated array) and MULTIPATH (a set of different inter-
28 faces to the same device).
29
30
31 R\bRA\bAI\bID\bD S\bSU\bUP\bPE\bER\bR B\bBL\bLO\bOC\bCK\bK
32 With the exception of Legacy Arrays described below, each
33 device that is incorportated into an MD array has a _\bs_\bu_\bp_\be_\br
34 _\bb_\bl_\bo_\bc_\bk written towards the end of the device. This
35 superblock records information about the structure and
36 state of the array so that the array an be reliably re-
37 assembled after a shutdown.
38
39 The superblock is 4K long and is written into a 64K
40 aligned block that start at least 64K and less than 128K
41 from the end of the device (i.e. to get the address of the
42 superblock round the size of the device down to a multiple
43 of 64K and then subtract 64K). The available size of each
44 device is the ammount of space before the super block, so
45 between 64K and 128K is lost when a device in incorporated
46 into an MD array.
47
48 The superblock contains, among other things:
49
50 LEVEL The
51
52 UUID a 128 bit Universally Unique Identifier that iden-
53 tifies the array that this device is part of.
54
55
56 L\bLI\bIN\bNE\bEA\bAR\bR
57 R\bRA\bAI\bID\bD0\b0
58 R\bRA\bAI\bID\bD1\b1
59 R\bRA\bAI\bID\bD4\b4
60 R\bRA\bAI\bID\bD5\b5
61 R\bRE\bEB\bBU\bUI\bIL\bLD\bD/\b/R\bRE\bES\bSY\bYN\bNC\bC
62 F\bFI\bIL\bLE\bES\bS
63 /\b/p\bpr\bro\boc\bc/\b/m\bmd\bds\bst\bta\bat\bt
64 Contains information about the status of currently
65 running array.
66
67 /\b/p\bpr\bro\boc\bc/\b/s\bsy\bys\bs/\b/d\bde\bev\bv/\b/r\bra\bai\bid\bd/\b/s\bsp\bpe\bee\bed\bd_\b_l\bli\bim\bmi\bit\bt_\b_m\bmi\bin\bn
68 A readable and writable file that reflects the cur-
69 rent goal rebuild speed for times when non-rebuild
70 activity is current on an array. The speed is in
71 Kibibytes per second, and is a per-device rate, not
72 a per-array rate (which means that an array with
73 more disc will shuffle more data for a given
74 speed). The default is 100.
75
76
77 /\b/p\bpr\bro\boc\bc/\b/s\bsy\bys\bs/\b/d\bde\bev\bv/\b/r\bra\bai\bid\bd/\b/s\bsp\bpe\bee\bed\bd_\b_l\bli\bim\bmi\bit\bt_\b_m\bma\bax\bx
78 A readable and writable file that reflects the cur-
79 rent goal rebuild speed for times when no non-
80 rebuild activity is current on an array. The
81 default is 100,000.
82
83
84 S\bSE\bEE\bE A\bAL\bLS\bSO\bO
85 m\bmd\bda\bad\bdm\bm(8), m\bmk\bkr\bra\bai\bid\bd(8).
86
87
88
89 MD(4)