trying to "brute-force" my RAID 5...

trying to "brute-force" my RAID 5...

[Sevrin Robstad]

I have written some posts about this before... My 6 disk RAID 5 broke 
down because of hardware failure. When I tried to get it up'n'running again
I did a --create without any missing disk, which made it rebuild. I have 
also lost all information about how the old RAID was set up..

I got a friend of mine to make a list of all the 6^6 combinations of dev 
1 2 3 4 5 missing, and set it up this way :

"mdadm --create -n 6 -l 5  dev1 2 3 4 5 missing ; fdisk -l /dev/md0 ; 
mdadm --stop /dev/md0" .
But a "cat logfile | grep Linux" of the output of this script tells me 
that on no of these combination does it find a valid "type 83" partition.

shouldn't this work ???

Sevrin

Re: trying to "brute-force" my RAID 5...

[Molle Bestefich]

Sevrin Robstad wrote:
> I got a friend of mine to make a list of all the 6^6 combinations of dev
> 1 2 3 4 5 missing,
>
> shouldn't this work ???

Only if you get the layout and chunk size right.

And make sure that you know whether you were using partitions (eg.
sda1) or whole drives (eg. sda - bad idea).

Re: trying to "brute-force" my RAID 5...

[Sevrin Robstad]

 Molle Bestefich wrote:

>> Sevrin Robstad wrote:
>>
>>> I got a friend of mine to make a list of all the 6^6 combinations of 
>>> dev
>>> 1 2 3 4 5 missing,
>>>
>>> shouldn't this work ???
>>
>>
>> Only if you get the layout and chunk size right.
>>
>> And make sure that you know whether you were using partitions (eg.
>> sda1) or whole drives (eg. sda - bad idea).
>>
> Thanks for replying.. I guess I'm pretty sure that ONE of the 66 
> combination should be the right one?? And chunk size - 64kbyte is 
> default, yes ? I created the RAID when I installed Fedora Core 3 some 
> time ago, didn't do anything special so the chunks should be 64kbyte 
> and parity should be left-symmetric ?
>  I'm also sure that I created it on partitions, and all disks has a 
> "Linux Raid" partition on it.
>
> But still, when I grep the log of my script I get no partition out of 
> any combination...
>
> Any Idea ?
>
>
> Sevrin

Re: trying to "brute-force" my RAID 5...

[Molle Bestefich]

Sevrin Robstad wrote:
> I created the RAID when I installed Fedora Core 3 some time ago,
> didn't do anything special so the chunks should be 64kbyte and
> parity should be left-symmetric ?

I have no idea what's default on FC3, sorry.

> Any Idea ?

I missed that you were trying to fdisk -l /dev/md0..
As others have suggested, search for filesystems using fsck, or mount,
or what not ;-).

Re: trying to "brute-force" my RAID 5...

[Neil Brown]

On Monday July 17, quackyo@start.no wrote:
> I have written some posts about this before... My 6 disk RAID 5 broke 
> down because of hardware failure. When I tried to get it up'n'running again
> I did a --create without any missing disk, which made it rebuild. I have 
> also lost all information about how the old RAID was set up..
> 
> I got a friend of mine to make a list of all the 6^6 combinations of dev 
> 1 2 3 4 5 missing, and set it up this way :
> 
> "mdadm --create -n 6 -l 5  dev1 2 3 4 5 missing ; fdisk -l /dev/md0 ; 
> mdadm --stop /dev/md0" .
> But a "cat logfile | grep Linux" of the output of this script tells me 
> that on no of these combination does it find a valid "type 83" partition.
> 
> shouldn't this work ???

No.

What are you expecting fdisk to tell you?  fdisk lists partitions and
I suspect you didn't have any partitions on /dev/md0
More likely you want something like
   fsck -n -f /dev/md0

and see which one produces the least noise.

NeilBrown

Re: trying to "brute-force" my RAID 5...

[Francois Barre]

> What are you expecting fdisk to tell you?  fdisk lists partitions and
> I suspect you didn't have any partitions on /dev/md0
> More likely you want something like
>    fsck -n -f /dev/md0
>
> and see which one produces the least noise.

Maybe a simple file -s /dev/md0 could do the trick, and would only
produce output different from the mere "data" when the good
configuration is found...

-- 
F.-E.B.

Re: trying to "brute-force" my RAID 5...

[Brad Campbell]

Francois Barre wrote:
>> What are you expecting fdisk to tell you?  fdisk lists partitions and
>> I suspect you didn't have any partitions on /dev/md0
>> More likely you want something like
>>    fsck -n -f /dev/md0
>>
>> and see which one produces the least noise.
> 
> Maybe a simple file -s /dev/md0 could do the trick, and would only
> produce output different from the mere "data" when the good
> configuration is found...
> 
More likely to produce an output whenever the 1st disk in the array is in the right place as it will 
just look at the 1st couple of sectors for the superblock.

I'd go with the fsck idea as it will try to inspect the rest of the filesystem also.

Brad
-- 
"Human beings, who are almost unique in having the ability
to learn from the experience of others, are also remarkable
for their apparent disinclination to do so." -- Douglas Adams

Re: trying to "brute-force" my RAID 5...

[Francois Barre]

> More likely to produce an output whenever the 1st disk in the array is in the right place as it will
> just look at the 1st couple of sectors for the superblock.
>
> I'd go with the fsck idea as it will try to inspect the rest of the filesystem also.
>

Obviously that's true, but it's still a good way to be sure of the
first disk, and the time cost of the file -s is
neglectible...Personally, I would have done both.

Re: trying to "brute-force" my RAID 5...

[Sevrin Robstad]

Neil Brown wrote:
 >
 >>I have written some posts about this before... My 6 disk RAID 5 broke
 >>down because of hardware failure. When I tried to get it up'n'running 
again
 >>I did a --create without any missing disk, which made it rebuild. I have
 >>also lost all information about how the old RAID was set up..
 >>
 >>I got a friend of mine to make a list of all the 6^6 combinations of dev
 >>1 2 3 4 5 missing, and set it up this way :
 >>
 >>"mdadm --create -n 6 -l 5  dev1 2 3 4 5 missing ; fdisk -l /dev/md0 ;
 >>mdadm --stop /dev/md0" .
 >>But a "cat logfile | grep Linux" of the output of this script tells me
 >>that on no of these combination does it find a valid "type 83" partition.
 >>
 >>shouldn't this work ???
 >
 > No.
 >
 > What are you expecting fdisk to tell you?  fdisk lists partitions and
 > I suspect you didn't have any partitions on /dev/md0
 > More likely you want something like
 >    fsck -n -f /dev/md0
 >
 > and see which one produces the least noise.

They all produce

"Bad magic number in super-block while trying to open /dev/md0" .

I tried file -s /dev/md0 also, and with one of the disk as first disk I 
got "ext 3 filedata (needs journal recovery) (errors)" .

but as fsck -n -f can't do anything with it, there might not be any hope ?


Or can it still be that I have some wrong setting?

Chunk size is (and was) default 64k, yes?

Sevrin

Re: trying to "brute-force" my RAID 5...

[Tuomas Leikola]

On 7/19/06, Sevrin Robstad <quack@online.no> wrote:
> I tried file -s /dev/md0 also, and with one of the disk as first disk I
> got "ext 3 filedata (needs journal recovery) (errors)" .

Congratulations, you have found your first disk. Does fsck still
complain about the magic number?