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Commit | Line | Data |
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56eb10c0 NB |
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) |