Re: Promise SATAII150 TX4 or raidreconf broken - answer

[Tyler <pml@dtbb.net>]

Eyal Lebedinsky wrote:

>Executive summary: it is not the TX4. It is not really raidreconf.
>You must specify the parity-algorithm in raidtab because the
>raidreconf default is not what one expects.
>
>I have now investigated the corrupted 3->4 disk raidreconf and I
>can see that there is a pattern to the problem. A similar pattern
>is seen with a 4->5 run.
>
>I wrote known values to the raid before the reconf and checked
>after. The process is
>	create /dev/md0
>	write to it
>	raidreconf it
>	read it and see which blocks show up where
>
>What I see is that the 2nd pair of each 6 blocks is swapped. Here
>is the error list for a test with 1 cyl (31 blocks) per disk:
>
>bad block 2 says it is 3
>bad block 3 says it is 2
>bad block 8 says it is 9
>bad block 9 says it is 8
>bad block 14 says it is 15
>bad block 15 says it is 14
>bad block 20 says it is 21
>bad block 21 says it is 20
>bad block 26 says it is 27
>bad block 27 says it is 26
>bad block 32 says it is 33
>bad block 33 says it is 32
>bad block 38 says it is 39
>bad block 39 says it is 38
>bad block 44 says it is 45
>bad block 45 says it is 44
>bad block 50 says it is 51
>bad block 51 says it is 50
>bad block 56 says it is 57
>bad block 57 says it is 56
>20 errors in 62 blocks
>
>At this point I decided that I must take the TX4 out of the equation.
>This is just too regular for a hardware problem. I created four
>partitions on one disk and repeated the test. It failed just the same.
>
>I was now reasonably convinced that it is raidreconf that gives me
>grief. Nevertheless, the pattern is just too regular. Maybe the program
>does not agree with md on the parity algorithm? The default is said
>to be left-symmetric (see man mdadm; man raidtab does not say), so I
>specified this explicitly in the raidtab and it started working.
>
>Good, but I needed to understand this.
>
>Looking at the raidtools code (where raidreconf is built), I think
>that it does not default to left-symmetric. It looks to me like the
>config struct is malloced and zeroed (with memset) meaning the .layout
>member is set to left-asymmetric (see top of parser.c) and I do not
>see that it is ever set to any other default (left-symmetric would
>be numeric 2).
>
>--
>Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.org/eyal/>
>	attach .zip as .dat
>
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>
Nice work Eyal :)

Now all we need is a patch for raid-reconf to fix default behaviour? :D

Regards,
Tyler.


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