[CentOS] 40TB File System Recommendations

On 4/13/11, Brandon Ooi <brandono at gmail.com> wrote:

> centos 5 can expand raid 0/1/5. just not 6. 10 is just layered 0/1 so you
> can expand it.
> centos 6 will be able to expand raid6 as it was a feature in 2.6.20 or
> something.

This is where I'm getting confused. I had been reading up on mdadm,
torn between using RAID 5/6 for the ability to grow the array with
more disks and RAID 10 for better IOPS. The man pages itself says that
"Currently  supported  growth options include changing the active size
of component devices and  changing  the  number  of  active devices
in RAID levels 1/4/5/6,"

Along with other internet sources seems to imply that growing RAID 0
is not supported, and by therefore by extension neither is RAID 10.
Furthermore, I read on Neil Brown's blog that reshaping RAID 10 was a
planned but not implemented feature.

Is the difference here between using mdadm to directly create a RAID
10 vs manually layering on RAID 0 on RAID 1 devices?

Or is the expansion here limited to replacing the existing components
drive with larger ones, e.g. replacing four 1TB drives with four 2TB
drives so going from a 2TB to 4TB array?