glabel, gmirror, and gpart

Warren Block wblock at
Sat Aug 27 13:18:23 UTC 2011

On Sat, 27 Aug 2011, Johan Hendriks wrote:

>> On Fri, Aug 26, 2011 at 11:04 PM, Warren Block <wblock at> wrote:
>> So it's cosmetic, but not really the kind of message that instills
>> confidence.  gptboot needs to be able to tell if it's reading from a
>> gmirror.  Or gmirror should provide one block less than it does, so it
>> doesn't overwrite the GPT backup.
> I use the whole disk to gmirror setup on all my servers.
> And one day i thought i could try the gpart stuff.
> I also saw the message at startup, and disgarded it.
> This was on 8.1
> But when i did an upgrade to 8.2 later on, the system could not boot.
> So i had to find another way.
> So i would not do it like you do now, it could turn against you in the long run.
> The thing i did was to mirror each partition.
> Like so
> that way it worked.
> Do not forget to make your second disk bootable also

That was the idea I had last night trying to go back to sleep.  Use 
gpart to partition the disks, and use gmirror to mirror the partitions. 
A little more setup, because you have to create multiple mirrors instead 
of one with partitions inside it.

It also addresses Adam's question.  For two dissimilar disks, create 
partitions of the same size and mirror them instead of the whole disk.

gmirror apparently doesn't keep a list of outstanding writes, so smaller 
mirrors should be faster to sync.

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