Hi,

Am Mittwoch, 10. November 2021, 14:09:53 CET schrieb Markus Hochholdinger:

Am Samstag, 24. März 2012, 21:47:15 CET schrieb Markus Hochholdinger:

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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 [off-list ref]:

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On Friday June 27, Markus@hochholdinger.net wrote:

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Am Freitag, 27. Juni 2008 08:51 schrieb NeilBrown:

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From: Chris Webb <redacted>

[..]

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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.

It is working es (I) expected till at least kernel 5.4.158.

It is not working with 5.10.x till 5.15.1.

On my old systems (kernel <= 5.4.x) after resizing one component
  mdadm -E /dev/xvda2
is able to see the moved superblock only after
  echo 0 > /sys/block/md2/md/rd0/size

On new systems (kernel >= 5.10.0) it doesn't matter if I issue
  echo 0 > /sys/block/md2/md/rd0/size
mdadm -E keeps complaining about no superblock on the grown device.
(The bitmap was removed before the echo 0 and I tried to remove the bitmap at 
all before resizing, still the same issue.)

It's only possible to remove the changed device and add with a full rebuild. 
But this isn't possible, if both devices were resized before. mdadm complains 
about no metadata available, no matter what I do while the md raid1 is still 
running (where is the superblock updated on the disks then?).

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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