Re: Raid5 reshape

["Nigel J. Terry" <nigel@nigelterry.net>]

Neil Brown wrote:
> On Thursday June 15, irule@irule.net wrote:
>   
>> Hello all,
>>
>> I'm sorry if this is a silly question, but I've been digging around for
>> a few days now and have not found a clear answer, so I'm tossing it out
>> to those who know it best.
>>
>> I see that as of a few rc's ago, 2.6.17 has had the capability of adding
>> additional drives to an active raid 5 array (w/ the proper ver of mdadm,
>> of course). I cannot, however, for the life of me find out exactly how
>> one goes about doing it! I would love if someone could give a
>> step-by-step on what needs to be changed in, say, mdadm.conf (if
>> anything), and what args you need to throw at mdadm to start the reshape
>> process.
>>
>> As a point of reference, here's my current mdadm.conf:
>>
>>
>> DEVICE /dev/sda1
>> DEVICE /dev/sdb1
>> DEVICE /dev/sdc1
>> ARRAY /dev/md0 devices=/dev/sda1,/dev/sdb1,/dev/sdc1 level=5 num-devices=3
>>
>>     
>
> May I suggest:
>
>    DEVICE /dev/sd?1
>    ARRAY /dev/md0 UUID=whatever
>
> it would be a lot safer.
>
>   
>> I will be adding the devices /dev/sde1 and /dev/sdf1 (when I can find
>> out how :)
>>     
>
>  mdadm /dev/md0 --add /dev/sde1 /dev/sdf1
>  mdadm --grow /dev/md0 --raid-disks=5
>
> NeilBrown
> -
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>   
This might be an even sillier question, but I'll ask it anyway...

If I add a drive to my RAID5 array, what happens to the ext3 filesystem 
on top of it? Does it grow automatically? Do I have to take some action 
to use the extra space?

Thanks

Nigel