Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/Documentation/md.txt
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
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Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
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File size: 4080 byte(s)
Tag kernel26-2.6.12-alx-r9
1 | Tools that manage md devices can be found at |
2 | http://www.<country>.kernel.org/pub/linux/utils/raid/.... |
3 | |
4 | |
5 | Boot time assembly of RAID arrays |
6 | --------------------------------- |
7 | |
8 | You can boot with your md device with the following kernel command |
9 | lines: |
10 | |
11 | for old raid arrays without persistent superblocks: |
12 | md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn |
13 | |
14 | for raid arrays with persistent superblocks |
15 | md=<md device no.>,dev0,dev1,...,devn |
16 | or, to assemble a partitionable array: |
17 | md=d<md device no.>,dev0,dev1,...,devn |
18 | |
19 | md device no. = the number of the md device ... |
20 | 0 means md0, |
21 | 1 md1, |
22 | 2 md2, |
23 | 3 md3, |
24 | 4 md4 |
25 | |
26 | raid level = -1 linear mode |
27 | 0 striped mode |
28 | other modes are only supported with persistent super blocks |
29 | |
30 | chunk size factor = (raid-0 and raid-1 only) |
31 | Set the chunk size as 4k << n. |
32 | |
33 | fault level = totally ignored |
34 | |
35 | dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1 |
36 | |
37 | A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this: |
38 | |
39 | e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro |
40 | |
41 | |
42 | Boot time autodetection of RAID arrays |
43 | -------------------------------------- |
44 | |
45 | When md is compiled into the kernel (not as module), partitions of |
46 | type 0xfd are scanned and automatically assembled into RAID arrays. |
47 | This autodetection may be suppressed with the kernel parameter |
48 | "raid=noautodetect". As of kernel 2.6.9, only drives with a type 0 |
49 | superblock can be autodetected and run at boot time. |
50 | |
51 | The kernel parameter "raid=partitionable" (or "raid=part") means |
52 | that all auto-detected arrays are assembled as partitionable. |
53 | |
54 | |
55 | Superblock formats |
56 | ------------------ |
57 | |
58 | The md driver can support a variety of different superblock formats. |
59 | Currently, it supports superblock formats "0.90.0" and the "md-1" format |
60 | introduced in the 2.5 development series. |
61 | |
62 | The kernel will autodetect which format superblock is being used. |
63 | |
64 | Superblock format '0' is treated differently to others for legacy |
65 | reasons - it is the original superblock format. |
66 | |
67 | |
68 | General Rules - apply for all superblock formats |
69 | ------------------------------------------------ |
70 | |
71 | An array is 'created' by writing appropriate superblocks to all |
72 | devices. |
73 | |
74 | It is 'assembled' by associating each of these devices with an |
75 | particular md virtual device. Once it is completely assembled, it can |
76 | be accessed. |
77 | |
78 | An array should be created by a user-space tool. This will write |
79 | superblocks to all devices. It will usually mark the array as |
80 | 'unclean', or with some devices missing so that the kernel md driver |
81 | can create appropriate redundancy (copying in raid1, parity |
82 | calculation in raid4/5). |
83 | |
84 | When an array is assembled, it is first initialized with the |
85 | SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor |
86 | version number. The major version number selects which superblock |
87 | format is to be used. The minor number might be used to tune handling |
88 | of the format, such as suggesting where on each device to look for the |
89 | superblock. |
90 | |
91 | Then each device is added using the ADD_NEW_DISK ioctl. This |
92 | provides, in particular, a major and minor number identifying the |
93 | device to add. |
94 | |
95 | The array is started with the RUN_ARRAY ioctl. |
96 | |
97 | Once started, new devices can be added. They should have an |
98 | appropriate superblock written to them, and then passed be in with |
99 | ADD_NEW_DISK. |
100 | |
101 | Devices that have failed or are not yet active can be detached from an |
102 | array using HOT_REMOVE_DISK. |
103 | |
104 | |
105 | Specific Rules that apply to format-0 super block arrays, and |
106 | arrays with no superblock (non-persistent). |
107 | ------------------------------------------------------------- |
108 | |
109 | An array can be 'created' by describing the array (level, chunksize |
110 | etc) in a SET_ARRAY_INFO ioctl. This must has major_version==0 and |
111 | raid_disks != 0. |
112 | |
113 | Then uninitialized devices can be added with ADD_NEW_DISK. The |
114 | structure passed to ADD_NEW_DISK must specify the state of the device |
115 | and it's role in the array. |
116 | |
117 | Once started with RUN_ARRAY, uninitialized spares can be added with |
118 | HOT_ADD_DISK. |