RE: [PATCH 07/14] FIX: Extend size of raid0 array

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On Thursday, April 19, 2012 11:24 PM NeilBrown <neilb@xxxxxxx> wrote:
> 
> On Thu, 19 Apr 2012 15:09:45 +0000 "Dorau, Lukasz"
> <lukasz.dorau@xxxxxxxxx>
> wrote:
> 
> > On Tuesday, April 17, 2012 4:53 AM NeilBrown wrote:
> > >
> > > On Fri, 13 Apr 2012 16:52:01 +0200 Adam Kwolek
> <adam.kwolek@xxxxxxxxx>
> > > wrote:
> > >
> > > > For raid0, takeover operation is required for size change.
> > > > Add takeover to degraded raid4 before size change and back to raid0
> after.
> > > > Array information has to be read again from md after takeover.
> > > >
> > > > Signed-off-by: Adam Kwolek <adam.kwolek@xxxxxxxxx>
> > > > ---
> > > >  Grow.c |   35 +++++++++++++++++++++++++++++++++++
> > > >  1 files changed, 35 insertions(+), 0 deletions(-)
> > > >
> > > > diff --git a/Grow.c b/Grow.c
> > > > index 8c7bafc..e8f6554 100644
> > > > --- a/Grow.c
> > > > +++ b/Grow.c
> > > > @@ -1626,6 +1626,7 @@ int Grow_reshape(char *devname, int fd, int
> > > quiet, char *backup_file,
> > > >  		long long orig_size = get_component_size(fd)/2;
> > > >  		long long min_csize;
> > > >  		struct mdinfo *mdi;
> > > > +		int raid0_takeover = 0;
> > > >
> > > >  		if (orig_size == 0)
> > > >  			orig_size = array.size;
> > > > @@ -1674,6 +1675,28 @@ int Grow_reshape(char *devname, int fd, int
> > > quiet, char *backup_file,
> > > >  				"2TB per device\n");
> > > >  			size = min_csize;
> > > >  		}
> > > > +		if (st->ss->external) {
> > > > +			if (sra->array.level == 0) {
> > > > +				rv = sysfs_set_str(sra, NULL, "level",
> > > > +						   "raid5");
> > > > +				if (!rv) {
> > > > +					raid0_takeover = 1;
> > > > +					/* get array parametes after takeover
> > > > +					 * to chane one parameter at time
> > > only
> > > > +					 */
> > > > +					rv = ioctl(fd, GET_ARRAY_INFO,
> > > &array);
> > > > +				}
> > > > +			}
> > > > +			/* make sure mdmon is
> > > > +			 * aware of the new level */
> > > > +			if (!mdmon_running(st->container_dev))
> > > > +				start_mdmon(st->container_dev);
> > > > +			ping_monitor(container);
> > > > +			if (mdmon_running(st->container_dev) &&
> > > > +					st->update_tail == NULL)
> > > > +				st->update_tail = &st->updates;
> > > > +		}
> > > > +
> > > >  		array.size = size;
> > > >  		if (array.size != size) {
> > > >  			/* got truncated to 32bit, write to
> > > > @@ -1686,12 +1709,24 @@ int Grow_reshape(char *devname, int fd,
> int
> > > quiet, char *backup_file,
> > > >  				rv = -1;
> > > >  		} else {
> > > >  			rv = ioctl(fd, SET_ARRAY_INFO, &array);
> > > > +
> > > >  			/* manage array size when it is managed externally
> > > >  			 */
> > > >  			if ((rv == 0) && st->ss->external)
> > > >  				rv = set_array_size(st, sra, sra->text_version);
> > > >  		}
> > > >
> > > > +		if (raid0_takeover) {
> > > > +			/* do not recync non-existing parity,
> > > > +			 * we will drop it anyway
> > > > +			 */
> > > > +			sysfs_set_str(sra, NULL, "sync_action", "idle");
> > >
> > > This is probably ineffective.  If the array thinks it needs to resync, then
> > > just setting it to 'idle' will only stop in temporarily.  It will immediately
> > > start syncing again.
> > >
> > > However given that it is a RAID5 array which is degraded, it shouldn't try
> to
> > > resync at all.
> > >
> > > So:  does it still work if you remove this line?  If so, could you send a
> > > patch to remove it?
> > > If not - we should work out why.
> > >
> >
> > It doesn't work without this line.
> > The N-disks raid0 changes to degraded (N+1)-disks raid5 (N of N+1 disks)
> > in /proc/mdstat after size extension, however the metadata on all disks is
> correct.
> >
> 
> In that case I suspect that fact that it works with the line is racy and it
> could sometimes fail.  Setting "sync_action" to "frozen" would be safer.
> Can you confirm that also works?  I'd feel more comfortable about that.
> 

You're right. I've checked it on another machine and it sometimes fails.
I've also checked that with "sync_action" set to "frozen" it works.
I'll send the patch soon.

Regards,
Lukasz



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