New BSD Installer

Miroslav Lachman 000.fbsd at
Fri Feb 17 17:10:15 UTC 2012

Pete French wrote:
>> I wasn't aware you could do that.  I was only aware that it was the
>> other way around.  That (my) misconception seems to also be relayed
>> by others such as Miroslav who said:
> Should this not be the recommended way of doing things even for MBR
> disks ? I have a lot of machines booting from gmirror, but we always
> do it by mirroring MBR partitions (or GPT ones). I cant see why you would
> want to do it the other way round in fact. It doesnt gain you anything
> does it ?

Yes it does? Am I the only one person on the whole earth seeing the big 
difference in easy setup of mirroring two drives instead of many 
individual partitions?

Freddie Cash already write about disk thrashing on rebuild after power 
failure, but initial setup or repair after disk replacement is also pain 
with mirroring individual partitions.

 > As someone else pointed out, you do need to partition the two drives
 > to match, and add bootloaders to them. But thats not really a great
 > hardship is it, and everything just works properly. You dont need
 > any different bootloader (as it sees the start of the drive and the
 > gmirror stuff is at the end).

Comparing our usual setup with 7 partitions after disk failure and 

Mirroring whole drives (after failed disk replacement):

1) gmirror forget -v gm0
2) gmirror insert -v gm0 ada1

And I am done!

Mirroring individual partitions (maintenance nightmare)):

  1) find sizes of partitions
  2) create partitions on new drive
  3) install boot sector
  4) gmirror forget -v gm0p1
  5) gmirror insert -v gm0p1 ada1p1 (and wait til synchronized)
  6) gmirror forget -v gm0p2
  7) gmirror insert -v gm0p2 ada1p2 (and wait til synchronized)
  8) gmirror forget -v gm0p3
  9) gmirror insert -v gm0p3 ada1p3 (and wait til synchronized)
10) gmirror forget -v gm0p4
11) gmirror insert -v gm0p4 ada1p4 (and wait til synchronized)
12) gmirror forget -v gm0p5
13) gmirror insert -v gm0p5 ada1p5 (and wait til synchronized)
14) gmirror forget -v gm0p6
15) gmirror insert -v gm0p6 ada1p6 (and wait til synchronized)
16) gmirror forget -v gm0p7
17) gmirror insert -v gm0p7 ada1p7

And after 15 more steps, you are done too.

I think you cannot compare mirrored partitions to what can be done by 
ZFS mirror or gmirror on whole drives and I am not willing to go by this 
way. I will use gmirror and MBR where possible.

Miroslav Lachman

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