Re: what happens to raid when more disks are added?

[Herta Van den Eynde <herta.vandeneynde@cc.kuleuven.ac.be>]

Paul Clements wrote:

>Herta Van den Eynde wrote:
> 
>  
>
>>To linux, they are known as devices sd[c-h], which have been configured
>>as raid 0+1:
>>
>># cat /proc/mdstat
>>Personalities : [raid0] [raid1]
>>read_ahead 1024 sectors
>>md2 : active raid1 md1[1] md0[0]
>>      106679168 blocks [2/2] [UU]
>>
>>md0 : active raid0 sde1[2] sdd1[1] sdc1[0]
>>      106679232 blocks 8k chunks
>>
>>md1 : active raid0 sdh1[2] sdg1[1] sdf1[0]
>>      106679232 blocks 8k chunks
>>
>>unused devices: <none>
>>    
>>
>
>It's generally thought to be better to set this up as a RAID 1+0 (three
>raid1 devices striped together) but maybe there's a reason why you've
>opted for the RAID 0+1? (there's one less md device, I guess)...
>
> 
>  
>
>>When I need to add extra disks, e.g. in slots 3 and 12, I assume that
>>the disk in slot 3 will get device name /dev/sdf, and the disks in slots
>>9 through 12 will subsequently be known as /dev/sd[g-j].  How will that
>>affect the raid 0+1 config?
>>    
>>
>
>You may want to think about using the autodetection feature of md (or
>mdadm's UUID capability)... these would allow you to avoid messing
>things up if your drive letters shift on you...
>
>--
>Paul
>  
>
Thanks, Paul.

Raid 1+0 definitely was and is on my wish list, but when I set up the 
initial systems, I had no time to play around and check things out.  I 
was nervous about the potential impact of devices changing names, and 
figured that it'd be easier to manage with a raid 0+1, as it'd be easy 
to break the mirror and take it from there.

I've got a bit more time now, so I'll check out autodetection and uuid.

Kind regards,

Herta


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Herta Van den Eynde
Toledo system management

K.U.Leuven - Ludit
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