mirroring existing boot drive sanity check

[David T-G <davidtg-robot@justpickone.org>]

Hi, all --

I think that this has been asked before, and so I think that I know 
where I'm
going, but before I take aim at my foot with a large-caliber mdadm ...  
:-)

I have an existing

   diskfarm:~ # parted /dev/sda unit MiB print free
   Model: ATA SanDisk SD6SB1M1 (scsi)
   Disk /dev/sda: 122104MiB
   Sector size (logical/physical): 512B/512B
   Partition Table: gpt
   Disk Flags: pmbr_boot

   Number  Start     End        Size      File system     Name           
Flags
           0.02MiB   1.00MiB    0.98MiB   Free Space
    1      1.00MiB   33793MiB   33792MiB  linux-swap(v1)  diskfarm-swap  
swap
    2      33793MiB  66561MiB   32768MiB  xfs             diskfarmsuse
    3      66561MiB  99329MiB   32768MiB                  diskfarmknop   
legacy_boot
    4      99329MiB  122104MiB  22775MiB  xfs             diskfarm-ssd

128G SSD.  I have obtained a shiny new

   diskfarm:~ # parted /dev/sde unit MiB print free
   Model: ATA SATA SSD (scsi)
   Disk /dev/sde: 244198MiB
   Sector size (logical/physical): 512B/512B
   Partition Table: gpt
   Disk Flags:

   Number  Start      End        Size       File system  Name           
Flags
           0.02MiB    1.00MiB    0.98MiB    Free Space
    1      1.00MiB    33793MiB   33792MiB                diskfarm-swap  
swap
    2      33793MiB   66561MiB   32768MiB                diskfarmsuse
    3      66561MiB   99329MiB   32768MiB                diskfarmknop   
legacy_boot
    4      99329MiB   122104MiB  22775MiB                diskfarm-ssd
           122104MiB  244198MiB  122094MiB  Free Space

256G SSD to use as a mirror.  [You can ignore the sgdisk-copied 
partition
layout for the moment; that was a false start.]  My final-view plan is, 
in
fact, to replace the 128 with another 256 and grow the -ssd data 
partition.

For a typical mirror-an-existing, I think that I need to create all of 
my
slices and the [degraded] mirror on the new, copy over the old, boot 
from new,
and then treat old as just another disk to shove in.  There's the 
question of
making partitions larger for the RAID superblock info, though, and -- 
and
here's where I get confused -- even on the old disk when adding it in.

As you can see, I have no free space on the little guy.  I was thinking 
I'd
bump my slices larger on the new disk so that I have room to spare to 
copy
everything over, with the data slice a little less larger than it would 
have
been, but then ... I think I saw that I need to make the 2nd-drive 
slices
larger, too, so what do I do with the old guy?

And, in fact, does it even matter?  If I understand this correctly, I'll 
be
running entirely from the new disk in the mirror once this is done, and 
so it
doesn't matter whether I put the little old or the other big new in to 
fill out
the mirror.  If that's the case, then I don't really care about 
partition size
because I'm going to start with mirrored partitions.

Oh, and just because I'm a glutton for punishment (even more than using 
this
stupid webmail because we're currently down my home directory disk on 
our mail
server and I'm impatient), if I'm essentially starting from scratch, 
should I
mirror the entire [yes, identical] drive and partition the metadevice,
*BSD-style, or mirror individual partitions?


Thanks as always!

:-D
-- 
David T-G
See http://justpickone.org/davidtg/email/
See http://justpickone.org/davidtg/tofu.txt