Re: waiting for recovery to complete

["Hervé Eychenne" <rv@eychenne.org>]

On Sun, Apr 17, 2005 at 10:49:14AM -0700, Tim Moore wrote:

 Hi,

> The recovery daemon adjusts reconstruction speed dynamically according to 
> available system resources.
> Disk I/O is somewhat slower but works just fine.  You don't have to wait.

So I don't have to wait to take the disk out, as the recovery will
continue with embedded disk battery and wireless bus connection?
How cool... ;-)

Well... more seriously, I can't believe this question doesn't raise
any interest, even if it seems like it does not. :-(
Does everyone really type cat /proc/mdstat from time to time??
How clumsy...
I just want to chat about the best way to add a backend for this kind
of feature, so we could implement that properly... (and yes, that is
definitely _nedded_ if you want to do things right)

 Herve

> Hervé Eychenne wrote:
> > Hi,
> >
> >Suppose I'm waiting for a recovery to be completed, and want to run a
> >command afterwards (halt, send a mail, or anything else...).
> >The most practiacl way I can see is to check /proc/mdstat.
> >
> >But what if I want to do that automatically (without bothering looking
> >at it manually from time to time)?
> >For example, one could do:
> ># while cat /proc/mdstat | grep recovery > /dev/null ; do sleep 5 ; done
> >
> >But that's quite ugly, as:
> >- it's an active polling, and it is time consuming (even if slightly)
> >- it may even be unreliable, as I guess one cannot ensure that /proc/mdstat
> >  will print the "recovery" string during the (very short, but well...)
> >  transition between two partitions to recover
> >
> >I think that a passive wait would be much better instead.
> >And ideally, we should have a simple and efficient way to let a program
> >know if a device is in a clean state (or being recovered), and another
> >that would wait until the device is clean (recovery finished).
> >
> >So, the while loop could be replaced by something like
> > mdadm --recovery-wait    (for example)
> >which would exit only when all pending recoveries have finished, and
> >let the script continue.
> >That would be much practical, reliable, and cleaner than a loop, don't you
> >think?
> >
> >How this could be achieved is another question... probably the best
> >would be that userspace can select on a file descriptor, or something
> >like that (netlink device?)
> >What do you think?
> >
> > Hervé

 Hervé

-- 
 _
(°=  Hervé Eychenne
//)  Homepage:          http://www.eychenne.org/
v_/_ WallFire project:  http://www.wallfire.org/

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