Re: Resurrecting a Dirty RAID-5

[Adam Goryachev <mailinglists@websitemanagers.com.au>]

On 13/07/15 01:01, jtroan@jt-sw.com wrote:
>> On Wed, 8 Jul 2015, jtroan@jt-sw.com wrote:
>>
>>> I'm also thinking about adding a fourth drive and try to config it as a
>>> hot-spare, giving me some extra margin for failure.
>> I would recommend you turn your raid5 into raid6 instead of having a
>> raid5+spare. This can be done with a fairly simple command, without
>> downtime.
>>
> I like the idea of using RAID-6 for / (for all the VMs under /var).  (I
> figure I'll probably still have to do a spare on my RAID-1 device
> for /boot .)
>
> What's the (mdadm?) command to convert an MD from RAID-5 to RAID-6?
>
I think the standard option would be to have a hot spare, and then 
something like:
mdadm /dev/mdX --grow --level=raid6

Also, for your raid1, never have a hot spare, just do this:
mdadm /dev/mdX --grow --raid-devices=3
Then you will always have all your data replicated on all three drives, 
so again, no hot spare required.

Also remember to duplicate the grub/whatever boot sector....

Regards,
Adam

-- 
Adam Goryachev Website Managers www.websitemanagers.com.au