Couple of questions.

Couple of questions.

[Brad Campbell]

1 - When adding 2 missing disks to a RAID-6 (let's say a 4 drive RAID-6 
that was created with only 2 disks initally) why does it sync the first, 
then sync the second rather than doing both together?
  ie mdadm --add /dev/md0 /dev/sd[ab]

2 - If a drive disappears how do I remove it from an array.
  Let's say I have a 10 drive RAID-6 that has an odd error on a disk. 
The disk goes away (sdl), the disk comes back as sdq as md is still 
hanging on to the name sdl. I add sdq to the array, but I can't remove 
sdl as it physically no longer exists. udev has removed the device node 
and mdadm can't remove it from the array as it can't tell what it was.

Like this :
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md0 : active raid6 sdq[10] sdc[0] sdd[6] sdl[1](F) sdh[9] sda[8] sde[7] 
sdg[5] sdb[4] sdf[3] sdm[2]
       7814078464 blocks super 1.2 level 6, 64k chunk, algorithm 2 
[10/10] [UUUUUUUUUU]

Nothing urgent, just musings after the last weeks oddities.

Regards,
Brad

Re: Couple of questions.

[Roman Mamedov]

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On Sun, 10 Apr 2011 00:14:56 +0800
Brad Campbell <lists2009@fnarfbargle.com> wrote:

> 2 - If a drive disappears how do I remove it from an array.
>   Let's say I have a 10 drive RAID-6 that has an odd error on a disk. 
> The disk goes away (sdl), the disk comes back as sdq as md is still 
> hanging on to the name sdl. I add sdq to the array, but I can't remove 
> sdl as it physically no longer exists. udev has removed the device node 
> and mdadm can't remove it from the array as it can't tell what it was.

Hello,

See man mdadm and search for "detached". Just noticed that today while looking
for something else.

-- 
With respect,
Roman

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Re: Couple of questions.

[NeilBrown]

On Sun, 10 Apr 2011 00:14:56 +0800 Brad Campbell <lists2009@fnarfbargle.com>
wrote:

> 1 - When adding 2 missing disks to a RAID-6 (let's say a 4 drive RAID-6 
> that was created with only 2 disks initally) why does it sync the first, 
> then sync the second rather than doing both together?
>   ie mdadm --add /dev/md0 /dev/sd[ab]

Because the devices are added one at a time and between the moment when sda
is added and when sdb is added a recovery starts.

mdadm should write 'frozen' the 'sync_action' before adding the devices, and
then 'idle' after adding them both.  But it doesn't yet.
You could...
  echo frozen > /sys/block/md0/md/sync_action
  mdadm /dev/md0 --add /dev/sd[ab]
  echo idle > /sys/block/md0/md/sync_action

NeilBrown


> 
> 2 - If a drive disappears how do I remove it from an array.
>   Let's say I have a 10 drive RAID-6 that has an odd error on a disk. 
> The disk goes away (sdl), the disk comes back as sdq as md is still 
> hanging on to the name sdl. I add sdq to the array, but I can't remove 
> sdl as it physically no longer exists. udev has removed the device node 
> and mdadm can't remove it from the array as it can't tell what it was.
> 
> Like this :
> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
> md0 : active raid6 sdq[10] sdc[0] sdd[6] sdl[1](F) sdh[9] sda[8] sde[7] 
> sdg[5] sdb[4] sdf[3] sdm[2]
>        7814078464 blocks super 1.2 level 6, 64k chunk, algorithm 2 
> [10/10] [UUUUUUUUUU]
> 
> Nothing urgent, just musings after the last weeks oddities.
> 
> Regards,
> Brad
> --
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