Re: mdadm --fail requires writeable drive.

[NeilBrown <neilb@suse.de>]

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On Wed, 13 Nov 2013 12:17:21 +0000 Benjamin ESTRABAUD <be@mpstor.com> wrote:

> Hi,
> 
> I noticed that mdadm --fail will only work if a disk is present and is 
> writeable.
> 
> mdadm's Manage.c seems to first make sure the drive can be "stat"ed 
> before proceeding (which will fail if the drive is gone), and then 
> seemingly try to write "Faulty" to the drive's superblock as well as 
> notifying MD of the drive failure.
> 
> However, in many cases, a drive must be set faulty because it has gone 
> offline. MD will do a very good job to set the drive faulty itself, 
> provided that IOs are running on the array. If no IOs are running on the 
> array, removing a drive and then trying to set it as failed will not 
> work. Trying to "-r" the drive will also fail since the drive is not yet 
> marked as failed, so deemed still in use.
> 
> Looking through the code it seemed to me that MD could be told to fail a 
> drive even if that drive was no longer present (the /dev/sdX device node 
> file still is in this case), in the same way as remove works. Would that 
> be possible? Am I missing something here?

Does
  mdadm /dev/mdXX --fail detached

do what you want?

NeilBrown

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