Thanks Munir. That's probably what I'll do since I want to run badblocks 
on each drive and that alone should take several days per drive... I was 
going to plug them into separate machines to do that but I may as well go 
one at a time.

On Tue, 29 Oct 2013, Munir Nassar wrote:

> On Tue, Oct 29, 2013 at 2:45 PM,  <tclug at freakzilla.com> wrote:
>> Ok, so right now I have a RAID5 array I created with mdadm. It uses four
>> identical HDDs, one of which is a spare obviously (which is good because I
>> had one fail).
>>
>> Anyway, sincethe enclosure I use can support 8 drives, I'm getting four more
>> HDDs (also identical to the first) and plan on adding them to the current
>> array.
>>
>> Now my hopefully silly question is, do I have to do anything special while
>> adding them, or does mdadm/whatever know which to add as "live" data and
>> which to add as spares? Can I just go "mdadm --add /dev/md0 /dev/sdf1" (and
>> then sdg1, sdh1 and sdi1)? Or do I have to do anything special?
>
> when you do that you will add those drives as spares, you will then
> have to restripe using something like:
> mdadm --grow /dev/md0 --raid-devices=4  (since your raid deviced is currently 3)
>
> and while you can probably go directly to 7, or 8 i would recommend
> being patient and doing it one at a time.
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