[CentOS] RAID questions

On 2/16/2017 9:18 PM, Keith Keller wrote:
> On 2017-02-15, John R Pierce<pierce at hogranch.com>  wrote:
>> On 2/14/2017 4:48 PM,tdukes at palmettoshopper.com  wrote:
>>
>>> 3 - Can additional drive(s) be added later with a changein RAID level
>>> without current data loss?
>> Only some systems support that sort of restriping, and its a dangerous
>> activity (if the power fails or system crashes midway through the
>> restriping operation, its probably not restartable, you quite likely
>> will lose the whole volume)
> Doesn't mdraid support changing RAID levels?  I think it will even do it
> reasonably safely (though still better not to have a power failure!).  I
> have a vague memory of adding a drive to a RAID5 and converting it to a
> RAID6 but I could be misremembering.

any such operation requires the entire raid to be re-slivered, stripe by 
stripe, as ALL the data moves around. on a large raid made from 
multi-terabyte drives, this would take DAYS.


-- 
john r pierce, recycling bits in santa cruz