Re: replacing drives

[Roberto Nunnari <roberto.nunnari@supsi.ch>]

Robin Hill wrote:
> On Wed May 08, 2013 at 04:19:33PM +0200, Roberto Nunnari wrote:
> 
>> Robin Hill wrote:
>>> On Fri May 03, 2013 at 06:28:02PM +0200, Roberto Nunnari wrote:
>>>
>>>> Robin Hill wrote:
>>>>> The safest option would be:
>>>>>  - add in the new disks
>>>>>  - partition to at least the same size as your existing partitions (they
>>>>>    can be larger)
>>>>>  - add the new partitions into the arrays (they'll go in as spares)
>>>>>  - grow the arrays to 4 members (this avoids any loss of redundancy)
>>>>>  - wait for the resync to complete
>>>>>  - install grub/lilo/syslinux to the new disks
>>>>>  - fail and remove the old disk partitions from the arrays
>>>>>  - shrink the arrays back down to 2 members
>>>>>  - remove the old disks
>>>>>
>>>>> Then, if you're keeping the same number of partitions but increasing the
>>>>> size:
>>>> Ok.. got here.
>>>>
>>>>>  - grow the arrays to fill the partitions
>>>>>  - grow the filesystems to fill the arrays
>>>> Now the scary part.. so.. here I believe I should give the following 
>>>> commands:
>>>>
>>>> mdadm --grow /dev/md0 --size=max
>>>> mdadm --grow /dev/md1 --size=max
>>>> mdadm --grow /dev/md2 --size=max
>>>>
>>> Yep, that's right. Make sure they've actually grown to the correct size
>>> before you progress though - I have had one occasion where using
>>> --size=max actually ended up shrinking the array and I had to manually
>>> work out the size to use in order to recover. That was using an older
>>> version of mdadm though, and I've not seen it happen since.
>>>
>>>> and after that
>>>>
>>>> fsck /dev/md0
>>>> fsck /dev/md1
>>>> fsck /dev/md2
>>>>
>>> You'll need 'fsck -f' here to force it to run.
>> humm.. as /dev/md0 is mounted on / I probably should boot from a cd, and 
>> run fsck and resize2fs from there.. maybe using UUIDs, right?
>>
> You can just skip the fsck and run resize2fs - it'll work fine on a
> mounted filesystem. It'll probably be safer to do it offline though.
> 
> Cheers,
>     Robin

I'd rather stay on the safe side.. how do I assemble the array if I boot 
from a cd?

something like:

mdadm --scan --assemble --uuid=a26bf396:31389f83:0df1722d:f404fe4c

would to the job and let me with a /dev/mdX I will be able to work with 
(fsck and resize2fs)?

Thank you.
Robi