Re: auto assemble in read-only mode?

[NeilBrown <neilb@suse.de>]

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On Tue, 7 Oct 2014 08:31:34 -0400 Errol Neal <eneal@businessgrade.com> wrote:

> On Tue, 10/07/2014 03:15 AM, NeilBrown <neilb@suse.de> wrote:
> > On Tue, 7 Oct 2014 02:56:31 -0400 Errol Neal <eneal@businessgrade.com> wrote:
> > 
> > > On Mon, 10/06/2014 09:06 AM, Errol Neal <eneal@businessgrade.com> wrote:
> > > > hi folks. is it possible to assemble an md device in read-only mode? 
> > > > after an array has been assembled, I know I can mark it as readonly with --misc -o /dev/md0 for example, but only after its been assembled it seems..
> > > > 
> > > 
> > > Hi again. No thoughts here? 
> > 
> > Not even 18 hours since you last asked - what do you thing this is? The
> > Internet :-)
> 
> HAHA. I tend to feel ignored on large mailing lists lol. Need to see my therapist again ;)
>  
> > 
> > > I'm need to run a RAID1 device on two independent nodes (shared storage) and I'd like to assemble the device on the "slave" node in read-only mode to prevent any sync actions and etc. 
> > 
> > Did you try adding the "--readonly" option to your --assemble command?
> > (Always best to report everything you tried and how it failed - requires less
> > guess work). 
>  
> I did that previously and mdadm told me that  "option --readonly not valid in assemble mode". E.g. "mdadm --assemble --scan --readonly". 

That tells me use are using a version of mdadm earlier than 3.3.
"--assemble --readonly" support was added for 3.3.

NeilBrown


> The readonly flag seems like it can only be used after a device has been assembled. So for example, after the device has been assembled, I can 
> run mdadm --misc -o /dev/md0 but that is not always safe for my use case. 
> 
> 
>  
> > I hope you don't expect too much of a filesystem mounted from such an array
> > while the  other node is writing to the array...
> > 
> 
> I don't. It will be read-only until the pacemaker RA promotes the slave. 
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