I've just had to recreate my raid5 device by using
mdadm --create --assume-clean -n4 -l5 -e1.2 -c64
in order to recover my data (because --assemble would not work with force etc.).
The problem:
* Data Offset in the new array is much larger.
* Internal Bitmap is starting at a different # sectors from superblock.
* Array Size is smaller though the disks are the same.
How can I get these to be the same as what they were in the original array???
I have tried to make sure that nothing gets written to the md device except the metadata during create.
All of these are important because the fs on top of the LVM on top of the md would need all the data it can to fsck properly and I don't want it starting on the wrong offset.
I am including the output from mdadm --examine from before and after the create
Originally...
>>> /dev/sdb5:
>>> Magic : a92b4efc
>>> Version : 1.2
>>> Feature Map : 0x1
>>> Array UUID : 42c56ea0:2484f566:387adc6c:b3f6a014
>>> Name : GATEWAY:127 (local to host GATEWAY)
>>> Creation Time : Sat Aug 22 09:44:21 2009
>>> Raid Level : raid5
>>> Raid Devices : 4
>>>
>>> Avail Dev Size : 586099060 (279.47 GiB 300.08 GB)
>>> Array Size : 1758296832 (838.42 GiB 900.25 GB)
>>> Used Dev Size : 586098944 (279.47 GiB 300.08 GB)
>>> Data Offset : 272 sectors
>>> Super Offset : 8 sectors
>>> State : clean
>>> Device UUID : f8ebb9f8:b447f894:d8b0b59f:ca8e98eb
>>>
>>> Internal Bitmap : 2 sectors from superblock
>>> Update Time : Fri Mar 19 00:56:15 2010
>>> Checksum : 1005cfbc - correct
>>> Events : 3796145
>>>
>>> Layout : left-symmetric
>>> Chunk Size : 64K
>>>
>>> Device Role : Active device 2
>>> Array State : .AA. ('A' == active, '.' == missing)
New...
/dev/sdb5:
Magic : a92b4efc
Version : 1.2
Feature Map : 0x1
Array UUID : 8588b69c:c0579680:8a63486a:cbcb0e7d
Name : GATEWAY:511 (local to host GATEWAY)
Creation Time : Tue Apr 6 01:53:25 2010
Raid Level : raid5
Raid Devices : 4
Avail Dev Size : 586097284 (279.47 GiB 300.08 GB)
Array Size : 1758290688 (838.42 GiB 900.24 GB)
Used Dev Size : 586096896 (279.47 GiB 300.08 GB)
Data Offset : 2048 sectors
Super Offset : 8 sectors
State : clean
Device UUID : 13d6a075:c1cad6dc:c13c3d98:e4b980e9
Internal Bitmap : 8 sectors from superblock
Update Time : Tue Apr 6 23:23:07 2010
Checksum : df3cb34f - correct
Events : 4
Layout : left-symmetric
Chunk Size : 64K
Device Role : Active device 2
Array State : .AAA ('A' == active, '.' == missing)
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