On 07-Apr-2010, at 4:25 AM, Neil Brown wrote:
> On Tue, 6 Apr 2010 23:37:02 +0530
> Anshuman Aggarwal <anshuman@xxxxxxxxxxxxx> wrote:
>
>> 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???
>
> Use the same version of mdadm and you used to originally create the array.
> Probably 2.6.9 from the data, though 3.1.1 seems to create the same layout.
> So anything before 3.1.2
>
> I really should write a "--recreate" for mdadm which uses whatever parameters
> if it finds already on the devices.
>
> NeilBrown
>
Since I already tried to recreate using 3.1.2, with super block 1.2, would it have overwritten much other data on the device? Also is the superblock format documented somewhere such as a graph explaining where what is stored?
Thanks,
>
>>
>> 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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