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Date: Thu, 24 Jul 2008 17:36:48 +0200
From: "exxs.net - matevz sernc-urban" <ms@exxs.net>
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Subject: Re: [linux-lvm] Every now and then LVM is not recognized - LVM2 on
	RAID10
References: <48871F04.9090002@exxs.net> <20080723173514.GC30203@soda.linbit>
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To: LVM general discussion and development <linux-lvm@redhat.com>

Lars Ellenberg schrieb:
> On Wed, Jul 23, 2008 at 02:07:32PM +0200, exxs.net - matevz sernc-urban wrote:
>>
>> i am running into a very interesting situation today, that our LVM  
>> metadata is recognized only sometimes. LVM was running fine for some  
>> weeks and now from today on running pvscan 10 times one after another i  
>> get about 4 positive and 6 negative results (its somehow a coincidence  
>> that LVM is recognized).
>>
...
>>
>> Any hints?
>>
>> Where should it look regarding "/dev/md2: No label detected" vs.  
>> "/dev/md2: lvm2 label detected"??
>>
>> It seems like RAID-10 is not sync'ed well maybe? But, mdstat reports all  
>> disks are up.
> 
> just a shot in the dark:
> 
> for dev in /dev/sd{a,b,c,d}5; do
> 	md5=$(dd if=$dev iflag=direct bs=1M count=1 | md5sum)
> 	echo "$dev: $md5"
> done

this is a RAID 10,f2 (with 2 far copies)
so the starting order of blocks is different on all 4 hdd's (and 
therefore all four md5's are different).

> 
> echo check > /sys/block/md2/md/sync_action
> 

i did this, and it finished without any failures - all disks are up and 
sync'ed again. RAID is therefore not a possible problem.

i must add that the logical volumes are in use and working. i just 
really do not want to reboot the machine as i suppose they couldn't be 
brought up again.

Any other hints of why sometimes i get "/dev/md2: No label detected" vs.
  "/dev/md2: lvm2 label detected"?

thanks in advance for any possible hints
mat