Re: [PATCH 018 of 29] md: Support changing rdev size on running arrays.

[Markus Hochholdinger <Markus@hochholdinger.net>]

Hi,

Am Samstag, 24. März 2012, 21:47:15 CET schrieb Markus Hochholdinger:
> it's been a long time, but today I tried again and had success!
> Am 28.06.2008 um 01:41 Uhr schrieb Neil Brown <neilb@suse.de>:
> > On Friday June 27, Markus@hochholdinger.net wrote:
> > > Am Freitag, 27. Juni 2008 08:51 schrieb NeilBrown:
> > > > From: Chris Webb <chris@arachsys.com>
> [..]
> > You don't want to "mdadm --grow" until everything has been resized.
> > First lvresize one disk, then write '0' to the .../size file.
> > Then do the same for the other disk.
> > Then "mdadm --grow /dev/mdX --size max".
> it works for me, if I do:
>   echo 0 > /sys/block/md2/md/rd0/size
>   mdadm --grow /dev/md2 --size=max
>   # till here, nothing happens
>   echo 0 > /sys/block/md2/md/rd1/size
>   mdadm --grow /dev/md2 --size=max
>   # rebuild of the added space begins

This has been working for me till at least kernel 4.19.x and I first recognized  
it not working anymore with kernel 5.10.x . So inbetween something changed 
regarding the resize and grow of md raid1 with superblock version 1.0.
The grow still works and a rebuild is done, but afterwards the superblock 
isn't created/moved to the new end of the devices. The raid1 works until you 
stop it, but you won't be able to re-assemble it (re-creating works). While 
re-creating I recognized the grown filesystem (after the raid1 was grown) was 
too large (fsck complained).

I already tracked it down to the version of the metadata/superblock. With 
version 1.0 (superblock at the end) the above fails and it looks like the 
superblock on the grown device is somehow there but with wrong informations 
(mdadm --zero-superblock has removed something while mdadm -D .. tells me, 
there's no superblock).

All works fine with superblock version 1.2 (superblock at the beginning).

Any ideas what could have changed so the grow feature for raid1 with 
superblock version 1.0 isn't working anymore?

For now the workaround is to really remove a grown device from the raid1 and 
do a full rebuild before re-adding the other grown device.

I'll test the different kernel versions to see, where/when this feature was 
lost.


> If I do only:
>   echo 0 > /sys/block/md2/md/rd0/size
>   echo 0 > /sys/block/md2/md/rd1/size
>   mdadm --grow /dev/md2 --size=max
> nothing will change.
> As I understand, with "echo 0" md sees the new size and only with --grow the
> superblock will be moved.
> I'm doing this with 2.6.32-5-xen-686 within Debian (squeeze) 6.0.
> Many thanks to you and all the other linux-raid developers for this feature!
> I'm very happy about this :-)


-- 
Mfg

Markus Hochholdinger