On Sun, 8 Dec 2013 11:53:00 -0600 Hai Wu [off-list ref] wrote:

I am wondering whether it is possible for mdadm to auto-rebuild a failed
raid1 driver upon its replacement with a new drive? The following lines
from some RedHat website URL seems to indicate vaguely that it might be possible:

Yes and no.
"yes" because it is certainly possible to arrange this,
"no" because it isn't just mdadm which does it.

When a drive is plugged in, udev notices and can run various commands to do
things with that device.  You need to get udev to run "mdadm -I $devname"
when a new device is plugged in.
The udev scripts which come with mdadm will only do that for new drives which
appear to be part of an array already.  You presumably want it to do that for
any new drive.  The change should be quite easy.

Secondly, you need to tell mdadm that it is OK to add a new device as a spare
to an array.  To see how to do this you need to read the documentation for
the "POLICY" command in mdadm.conf.5.

A line like:
    POLICY action=force-spare
tells mdadm that any device passed to "mdadm -I" can be added to any array as
a spare.  You might not want that, but you can restrict it in various ways.

    POLICY path=pci-0000:00:1f.2-scsi* action=spare

says that any device attached to a particular controller can be added to any
array as long as it is already a member of the array, or appears to be blank.

There are various other directives which should allow you to describe
whatever you want.

NeilBrown

Previously, mdadm was not able to rebuild newly-connected drives
automatically. This update adds the array auto-rebuild feature and allows a
RAID stack to automatically rebuild newly-connected drives.

The goal is to get mdadm software raid1 to behave the same as hardware
raid1, when replacing failed hard drive. It should automatically detect new
drive and rebuild the new drive into part of raid1 ..--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html