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List:       linux-raid
Subject:    Re: Raidtab recreation?
From:       Thomas Waldmann <tw () waldmann-edv ! de>
Date:       2001-05-23 18:48:26
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> Could /etc/raidtab be recreated by some script/utility to reflect the
> actual situation? Such an utility would be really usefull...

No "ready to use" utility, but this command is quite useful for getting
infos out of the RAID 0.90 superblock:

dd if=/dev/sda3 bs=1k skip=22425536 count=4 | od -Ax -tx4 | less

Please be careful when using dd! Typos may easily destroy data, so think
twice and read the man page before!

sda3:  a raid partition

22425536 : the "sb offset" like a RAID kernel tells you (just an example,
this will vary) - unit of offset is 1k blocks

od ... : hexdump with u32 grouping

You will see:

at offset 0x0000 := u32 0xa92b4efc (magic)

at offset 0x0100 == u32 parity algorithm
                    LEFT-ASYMMETRIC       0
                    RIGHT-ASYMMETRIC      1
                    LEFT-SYMMETRIC        2
                    RIGHT-SYMMETRIC       3

at offset 0x0104 == u32 chunk size [bytes]
                    e.g. 0x00001000 -> 4k -> raidtab: chunk-size 4

The other infos are also there - somewhere in the hex dump.

But maybe you just remember which partition was which raid disk and just

the algorithm and chunk size is in question ...

For more infos just read the source of raidtools, esp. the header files.

Thomas



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