Re: Deleting mdadm RAID arrays

[Bill Davidsen <davidsen@tmr.com>]

Marcin Krol wrote:
> Thursday 07 February 2008 03:36:31 Neil Brown napisał(a):
>
>   
>>>    8     0  390711384 sda
>>>    8     1  390708801 sda1
>>>    8    16  390711384 sdb
>>>    8    17  390708801 sdb1
>>>    8    32  390711384 sdc
>>>    8    33  390708801 sdc1
>>>    8    48  390710327 sdd
>>>    8    49  390708801 sdd1
>>>    8    64  390711384 sde
>>>    8    65  390708801 sde1
>>>    8    80  390711384 sdf
>>>    8    81  390708801 sdf1
>>>    3    64   78150744 hdb
>>>    3    65    1951866 hdb1
>>>    3    66    7815622 hdb2
>>>    3    67    4883760 hdb3
>>>    3    68          1 hdb4
>>>    3    69     979933 hdb5
>>>    3    70     979933 hdb6
>>>    3    71   61536951 hdb7
>>>    9     1  781417472 md1
>>>    9     0  781417472 md0
>>>       
>> So all the expected partitions are known to the kernel - good.
>>     
>
> It 's not good really!!
>
> I can't trust /dev/sd* devices - they get swapped randomly depending 
> on sequence of module loading!! I have two drivers, ahci for onboard
> SATA controllers and sata_sil for additional controller.
>
> Sometimes the system boots ahci first and sata_sil later, sometimes 
> in reverse sequence. 
>
> Then, sda becomes sdc, sdb becomes sdd, etc. 
>
> It is exactly the problem that I cannot rely on kernel's information which
> physical drive is which logical drive!
>
>   
>> Then
>>   mdadm /dev/md0 -f /dev/d_1
>>
>> will fail d_1, abort the recovery, and release d_1.
>>
>> Then
>>   mdadm --zero-superblock /dev/d_1
>>
>> should work.
>>     
>
> Thanks, though I managed to fail the drives, remove them, zero superblocks 
> and reassemble the arrays anyway. 
>
> The problem I have now is that mdadm seems to be of 'two minds' when it comes 
> to where it gets the info on which disk is what part of the array. 
>
> As you may remember, I have configured udev to associate /dev/d_* devices with
> serial numbers (to keep them from changing depending on boot module loading 
> sequence). 
>
>   
Why do you care? If you are using UUID for all the arrays and mounts 
does this buy you anything? And more to the point, the first time a 
drive fails and you replace it, will it cause you a problem? Require 
maintaining the serial to name data manually?

I miss the benefit of forcing this instead of just building the 
information at boot time and dropping it in a file.

> Now, when I swap two (random) drives in order to test if it keeps device names 
> associated with serial numbers I get the following effect:
>
> 1. mdadm -Q --detail /dev/md* gives correct results before *and* after the swapping:
>
> % mdadm -Q --detail /dev/md0
> /dev/md0:
> [...]
>     Number   Major   Minor   RaidDevice State
>        0       8        1        0      active sync   /dev/d_1
>        1       8       17        1      active sync   /dev/d_2
>        2       8       81        2      active sync   /dev/d_3
>
> % mdadm -Q --detail /dev/md1
> /dev/md1:
> [...]
>     Number   Major   Minor   RaidDevice State
>        0       8       49        0      active sync   /dev/d_4
>        1       8       65        1      active sync   /dev/d_5
>        2       8       33        2      active sync   /dev/d_6
>
>
> 2. However, cat /proc/mdstat gives shows different layout of the arrays!
>
> BEFORE the swap:
>
> % cat mdstat-16_51
> Personalities : [raid6] [raid5] [raid4]
> md1 : active raid5 sdb1[2] sdf1[0] sda1[1]
>       781417472 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>
> md0 : active raid5 sde1[2] sdc1[0] sdd1[1]
>       781417472 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>
> unused devices: <none>
>
>
> AFTER the swap:
>
> % cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md1 : active(auto-read-only) raid5 sdd1[0] sdc1[2] sde1[1]
>       781417472 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>
> md0 : active(auto-read-only) raid5 sda1[0] sdf1[2] sdb1[1]
>       781417472 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
>
> unused devices: <none>
>
> I have no idea now if the array is functioning (it keeps the drives
> according to /dev/d_* devices and superblock info is unimportant)
> or if my arrays fell apart because of that swapping. 
>
> And I made *damn* sure I zeroed all the superblocks before reassembling 
> the arrays. Yet it still shows the old partitions on those arrays!
>   
As I noted before, you said you had these on whole devices before, did 
you zero the superblocks on the whole devices or the partitions? From 
what I read, it was the partitions.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 



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