[GLLUG] Advice on expanding an existing RAID 1 installation

[John Winters]

On 26/05/14 18:50, Iain M Conochie wrote:
> On 24/05/14 11:12, John Winters wrote:
>> Dear GLLUGers,
>
> Hi John
>>
>> I seek a spot of advice on enhancing an existing RAID 1 installation
>> (used for backing up all sorts of systems).
>>
>> The current system has 2 x 1TB drives in a RAID 1 configuration. These
>> are running out of space.
>>
>> I intend to get 3 x 3TB drives and would like to transfer everything
>> to those.
>>
>> The Linux RAID Wiki has a page on extending an existing RAID array,
>> but says I should start by removing one of my existing drives.
>> Presumably this isn't necessary if I have a spare physical
>> slot/controller slot/power lead?  Rather than their proposed approach
>> of remove=>add=>remove=>add, is there any reason I can't do
>> add=>remove=>add=>remove?
>
> Why would you want to extend it? You could create a new array that would
> use the entire space; I am pretty sure any RAID implementation will use
> the smallest device size for the size of the array, so adding a 3TB
> device into a 1TB array will not utilize 3TB.

True, but once you have replaced all the 1TB drives with 3TB ones, you 
can enlarge the RAID device.

> You could remove 1 x 1TB
> drive and replace with 2 x 3 TB drives, create a new array, and the copy
> over the data.

You could, but I doubt you'd find a faster way of copying the data than 
using the inbuilt facilities of RAID.

In this particular case, there are a very large number of files with 
multiple hard links, so copying them gets quite interesting.

John