Re: A few mdadm questions

[Robert Osiel <bob@osiel.org>]

Guy,

Thanks for the input.  I'm not sure why that disk is now a spare 
either.  I was hoping that there was some way to re-write that 
superblock to convince the array it was a good disk.  I saw some old 
(pre-mdadm) advice which mentioned using mkraid to rewrite (all) of the 
superblocks, but that seems really drastic.

In the worst case, as you mentioned, I would try to start with the other 
(failed) disk.  Most of the data on that drive is fairly static, so I 
hope to have some good recovery -- assuming the disk is still OK (in the 
past it has been something like a loose cable, so I'm hopeful).

I'll wait and see if Neil has any advice. *crosses fingers*

Bob


Guy wrote:

>Your array had 5 disks, not counting any spares.
>You need to start the array with at least 4 of the five disks, spares don't
>help when starting an array.
>
>I don't know why it thinks your disk (hdi1) is a spare.  But, that may
>explain how it was removed from the array.  Unless Neil has some magic
>incantations, I think you are out of luck.
>
>If Neil has no ideas, you could try to start the array with the drive that
>failed (hdk1), but that will cause corruption of any stripes that have
>changed since the drive was removed from the array.  So, save this option as
>a last resort.  Of course, if hdk1 has failed hard, you will not be able to
>use it.
>
>Last resort!!!  Corruption will occur!
>mdadm --assemble --force /dev/md0 /dev/hde1 /dev/hdk1 /dev/hdm1 /dev/hdo1
>
>Guy
>
>-----Original Message-----
>From: linux-raid-owner@vger.kernel.org
>[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Robert Osiel
>Sent: Saturday, November 13, 2004 7:36 PM
>To: linux-raid@vger.kernel.org
>Subject: Re: A few mdadm questions
>
>Guy/Neil:
>
>Thanks a lot for the help.
>Sorry that I didn't include all of the info in my last message, but this 
>box is off the network right now and doesn't even have a floppy or 
>monitor, so I had to do a little work to get the info out.
>
>I tried to start the array with the 3 good disks and the 1 spare, but I 
>got an error to the effect that 3 good + 1 spare drives are not enough 
>to start the array (see below)
>
> > cat /proc/mdstat
>Personalities : [linear] [raid0] [raid1] [raid5]  [multipath]
>read_ahead not set
>unused devices: <none>
>
> > mdadm -D /dev/md0
>mdadm: md device /dev/md0 does not appear to be active
>
> > mdadm --assemble --force /dev/md0 /dev/hde1 /dev/hdi1 /dev/hdm1 /dev/hdo1
>mdadm: /dev/md0 assembled from 3 drives and 1 spare - not enough to 
>start the array
>
> > cat /proc/mdstat
>Personalities : [linear] [raid0] [raid1] [raid5]  [multipath]
>read_ahead not set
>md0: inactive
>ide/host2/bus0/target0/lun0/part1[0]
>ide/host4/bus0/target0/lun0/part1[5]
>ide/host6/bus1/target0/lun0/part1[4]
>ide/host6/bus0/target0/lun0/part1[3]
>
>Some notes:
>hdk1 is the disk which failed initially
>hdi1 is the disk which I removed and which thinks it is a 'spare'
>
>The other three drives report basically identical info, like this:
> > mdadm -E /dev/hde1
>
>Magic : a92b4efc
>Version : 00.90.00
>UUID : ec2e64a8:fffd3e41:ffee5518:2f3e858c
>Creation Time : Sun Oct 5 01:25:49 2003
>Build Level: raid5
>Device Size : 160079488 (152.66 GiB 163.92 GB)
>Raid Devices : 5
>Total Devices : 5
>Preferred Minor : 0
>
>Update Time Sat Sep 25 22:07:26 2004
>State : dirty
>Active Devices : 3
>Working Devices : 4
>Failed Devices : 1
>Spare Devices : 1
>Checksum : 4ee5cc77 - correct
>Events : 0.10
>
>Layout : left-symmetric
>Chunk Size :  128K
>
>    Number        Major    Minor    RaidDevice    State
>this    0        22        1        0        active sync
>0        0        22        1        0        active sync
>1        1        0        0        1        faulty removed
>2        2        56        1        2        faulty 
>/dev/ide/host4/bus0/target0/lun0/part1
>3        3        57        1        3        active sync    
>/dev/ide/host4/bus1/target0/lun0/part1
>4        4        88        1        4        active sync 
>/dev/ide/host6/bus0/target0/lun0/part1
>5        5        34        1        5        spare
>
>Here are the two drives in question:
>
>__________mdadm -E /dev/hdi1:
>
>Magic : a92b4efc
>Version : 00.90.00
>UUID : ec2e64a8:fffd3e41:ffee5518:2f3e858c
>Creation Time : Sun Oct 5 01:25:49 2003
>Build Level: raid5
>Device Size : 160079488 (152.66 GiB 163.92 GB)
>Raid Devices : 5
>Total Devices : 5
>Preferred Minor : 0
>
>Update Time Sat Sep 25 22:07:26 2004
>State : dirty
>Active Devices : 3
>Working Devices : 4
>Failed Devices : 1
>Spare Devices : 1
>Checksum : 4ee5cc77 - correct
>Events : 0.10
>
>Layout : left-symmetric
>Chunk Size :  128K
>
>    Number        Major    Minor    RaidDevice    State
>this    5        34        1        5        spare
>0        0        22        1        0        active sync
>1        1        0        0        1        faulty removed
>2        2        56        1        2        faulty 
>/dev/ide/host4/bus0/target0/lun0/part1
>3        3        57        1        3        active sync    
>/dev/ide/host4/bus1/target0/lun0/part1
>4        4        88        1        4        active sync 
>/dev/ide/host6/bus0/target0/lun0/part1
>5        5        34        1        5        spare
>
>
>__________mdadm -E /dev/hdk1
>Magic : a92b4efc
>Version : 00.90.00
>UUID : ec2e64a8:fffd3e41:ffee5518:2f3e858c
>Creation Time : Sun Oct 5 01:25:49 2003
>Build Level: raid5
>Device Size : 160079488 (152.66 GiB 163.92 GB)
>Raid Devices : 5
>Total Devices : 5
>Preferred Minor : 0
>
>Update Time Sat Sep 25 22:07:24 2004
>State : dirty
>Active Devices : 4
>Working Devices : 5
>Failed Devices : 0
>Spare Devices : 1
>Checksum : 4ee5cc77 - correct
>Events : 0.9
>
>Layout : left-symmetric
>Chunk Size :  128K
>
>    Number        Major    Minor    RaidDevice    State
>this    2        56        1        2        active sync 
>/dev/ide/host4/bus0/target0/lun0/part1
>0        0        22        1        0        active sync
>1        1        0        0        1        faulty removed
>2        2        56        1        2        active sync 
>/dev/ide/host4/bus0/target0/lun0/part1
>3        3        57        1        3        active sync    
>/dev/ide/host4/bus1/target0/lun0/part1
>4        4        88        1        4        active sync 
>/dev/ide/host6/bus0/target0/lun0/part1
>5        5        34        1        5        spare
>
>
>
>
>Neil Brown wrote:
>
>  
>
>>On Friday November 12, bugzilla@watkins-home.com wrote:
>> 
>>
>>    
>>
>>>First, stop using the old raid tools.  Use mdadm only!  mdadm would not
>>>      
>>>
>have
>  
>
>>>allowed your error to occur.
>>>   
>>>
>>>      
>>>
>>I'm afraid this isn't correct, though the rest of Guy's advice is very
>>good (thanks Guy!).
>>
>> mdadm --remove
>>does exactly the same thing as
>> raidhotremove
>>
>>It is the kernel that should (and does) stop you from hot-removing a
>>device that is working and active.  So I'm not quite sure what
>>happened to Robert...
>>
>>Robert: it is always useful to provide specific with the output of 
>>   cat /proc/mdstat
>>and
>>   mdadm -D /dev/mdX
>>
>>This avoids possible confusion over terminology.
>>
>>NeilBrown
>> 
>>
>>    
>>
>
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