On 11/10/2017 02:22 PM, Jun-Kai Teoh wrote:

quoted

On Nov 10, 2017, at 11:04 AM, Phil Turmel [off-list ref]
wrote:

On 11/10/2017 01:15 PM, Jun-Kai Teoh wrote:

quoted

I'm backing up as much as I can, but I don't think I'll be able
to back up everything. I can back up very little of the data, so
I'm trying to prioritize carefully right now.

Ah, ok.  Well, after you get the important stuff backed up, you
can add more devices as spares and try to let MD continue its grow
and rebuild operations.  It might end up completing.

Again, pardon me if I sound super ignorant, I just want to do all of
this right.

Do I just plug in another blank 4TB, and run "mdadm -A /dev/md126
/dev/sd[newdrive]" into it?

Or leave it as it is, and just ask it to continue growing with "mdadm
-A -R", and *then* add a blank drive into the raid but don't ask it
to grow?

Neither....  With your array mounted and running as it is right now, but
after all backups are done, use:

    mdadm --add /dev/mdXXX /dev/sdX1

with the new device's *partition*.

MD should recognize the opportunity to proceed and will resume
rebuilding and growing.

quoted

But don't add any more complete devices to the array -- use a
partition that starts at 1MB and covers the rest of the device
(default for most partition tools nowadays).

Where can I read about how to do this properly? I tried googling it
but I'm pretty lost. Or what tool I should use etc.

parted or gdisk or a very modern version of fdisk will let you partition
your new drives.  They will default to a "GPT" disk label and will
generally place the first partition you create in the "right" place -- a
multiple of 4K, typically 1MB.  When you save the new partition table
(aka disk label), the #1 partition will show up in your list of devices.

quoted

I recommend that when/if your array is stable again, you add one
more spare (with partition) and then use mdadm's --replace
operation to move complete-device members to the new member.  When
each is done, take the newly freed device and partition it and do
the next.  When you have no more complete-device members and have
the last freed device partitioned, consider converting to raid6
with that spare.

I think I understand what you mean here, but it sounds like I need to
figure out the top two parts first and that'll take me awhile.

Same partitioning procedure for each free disk.

I'll probably have questions again, later, haha.

Sure, no problem.

I really appreciate all the support and patience from this list.

Y'all lifesavers.

You're welcome.

Phil