RAID superblock formats
From Linux Raid Wiki
(Difference between revisions)
| Line 154: | Line 154: | ||
<td>(signed)</td> | <td>(signed)</td> | ||
<td>This is only valid if<br>feature_map[0] is set<br><br>Signed value allows bitmap<br>to appear before<br>superblock on the disk</td> | <td>This is only valid if<br>feature_map[0] is set<br><br>Signed value allows bitmap<br>to appear before<br>superblock on the disk</td> | ||
| + | </tr> | ||
| + | <tr><td colspan="8"> </td></tr> | ||
| + | <tr> | ||
| + | <td colspan="8">Special Section: for RAID-Reshape</td> | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
| Line 160: | Line 164: | ||
<td>4</td> | <td>4</td> | ||
<td>new_level</td> | <td>new_level</td> | ||
| − | <td>(Used with RESHAPE)<br></td> | + | <td>(Used with RESHAPE)<br>the new RAID level being reshaped-to</td> |
<td>__u32</td> | <td>__u32</td> | ||
| − | <td> | + | <td>See field named<br>"level" above</td> |
<td>(Only valid if<br>feature bit '4'<br>is set)</td> | <td>(Only valid if<br>feature bit '4'<br>is set)</td> | ||
</tr> | </tr> | ||
| Line 215: | Line 219: | ||
<td>Always set to<br>zero when writing</td> | <td>Always set to<br>zero when writing</td> | ||
</tr> | </tr> | ||
| − | + | <tr><td colspan="8"> </td></tr> | |
<tr><td>Remaining section hasn't been added to the wiki yet</td></tr> | <tr><td>Remaining section hasn't been added to the wiki yet</td></tr> | ||
<tr> | <tr> | ||
Revision as of 18:51, 22 February 2008
Currently, the Linux RAID subsystem recognizes two distinct variant superblocks.
They are known as v0.9 and v1.x Superblock formats.
The v1.x Superblock format is as follows:
| Offset (Hex) | Offset (Dec) | Length (in bytes) |
Field Name | Usage/Meaning | Data Type | Data Value | Notes | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0x00 | 0 | 4 | magic | "Magic Number" (Superblock ID) |
__u32 | 0xa92b4efc (little-endian) |
|||||||||||||
| 0x04 | 4 | 4 | major_version | Major Version of the Superblock |
__u32 | 1 | |||||||||||||
| 0x08 | 8 | 4 | feature_map | Feature Map | __u32 | 0 (reserved) |
|||||||||||||
| 0x0c | 12 | 4 | pad0 | Padding Block | __u32 | 0 | Always set to zero when writing |
||||||||||||
| 0x10 | 16 | 16 | set_uuid | UUID for the Array(?) | __u8[16] | Set by user-space formatting util |
|||||||||||||
| 0x20 | 32 | 32 | set_name | Name for the Array(?) | char[32] | Set and used by user-space utils |
Nt | ||||||||||||
| 0x40 | 64 | 8 | ctime | Creation Time(?) | __u64 | low 40-bits are seconds high 24-bits are uSeconds |
|||||||||||||
| 0x48 | 72 | 4 | level | RAID Level of the Array |
__u32 |
|
RAID-6 not mentioned in the mdadm source(?) |
||||||||||||
| 0x4c | 76 | 4 | layout | layout of array (RAID5 only) |
__u32 | (?) | Only used for RAID5 |
||||||||||||
| 0x50 | 80 | 8 | size | used-size of component devices | __u64 | size of component devices (in # of 512-byte sectors) |
|||||||||||||
| 0x58 | 88 | 4 | chunksize | chunk-size of the array | __u32 | chunk-size of the array (in # of 512-byte sectors) |
|||||||||||||
| 0x8c | 92 | 4 | raid_disks | (?)number of disks in array(?) | __u32 | # | |||||||||||||
| 0x90 | 96 | 4 | bitmap_offset | # of sectors after superblock that bitmap starts (See note about signed value) |
__u32 | (signed) | This is only valid if feature_map[0] is set Signed value allows bitmap to appear before superblock on the disk |
||||||||||||
| Special Section: for RAID-Reshape | |||||||||||||||||||
| 0x94 | 100 | 4 | new_level | (Used with RESHAPE) the new RAID level being reshaped-to |
__u32 | See field named "level" above |
(Only valid if feature bit '4' is set) |
||||||||||||
| 0x98 | 104 | 8 | reshape_position | (Used with RESHAPE) Next address of the array to reshape |
__u64 | current position of the reshape operation | (Only valid if feature bit '4' is set) |
||||||||||||
| 0xa0 | 112 | 4 | delta_disks | (Used with RESHAPE) this holds the change in # of raid disks |
__u32 | change in # of raid disks | (Only valid if feature bit '4' is set) |
||||||||||||
| 0xa4 | 116 | 4 | new_layout | (Used with RESHAPE) |
__u32 | new layout for array | (Only valid if feature bit '4' is set) |
||||||||||||
| 0xa8 | 120 | 4 | new_chunk | (Used with RESHAPE) |
__u32 | new chunk size (See ) |
(Only valid if feature bit '4' is set) |
||||||||||||
| 0xac | 124 | 4 | pad1 | Padding Block #1 | __u8[4] | 0 | Always set to zero when writing |
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| Remaining section hasn't been added to the wiki yet | |||||||||||||||||||
| Oh | Od | Lb | Fn | Fm | Dt | Dv | Nt | ||||||||||||
