md/raid5: don't include 'spare' drives when reshaping to fewer devices. (3424bf6a) · Commits · 戴 / test

There are few situations where it would make any sense to add a spare when reducing the number of devices in an array, but it is conceivable: A 6 drive RAID6 with two missing devices could be reshaped to a 5 drive RAID6, and a spare could become available just in time for the reshape, but not early enough to have been recovered first. 'freezing' recovery can make this easy to do without any races. However doing such a thing is a bad idea. md will not record the partially-recovered state of the 'spare' and when the reshape finished it will think that the spare is still spare. Easiest way to avoid this confusion is to simply disallow it. Signed-off-by:

NeilBrown <neilb@suse.de>

drivers/md/raid5.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -5526,7 +5526,12 @@ static int raid5_start_reshape(mddev_t *mddev)

		/* Add some new drives, as many as will fit.
		* We know there are enough to make the newly sized array work.
		* Don't add devices if we are reducing the number of
		* devices in the array. This is because it is not possible
		* to correctly record the "partially reconstructed" state of
		* such devices during the reshape and confusion could result.
		*/
		if (mddev->delta_disks >= 0)
		list_for_each_entry(rdev, &mddev->disks, same_set)
		if (rdev->raid_disk < 0 &&
		!test_bit(Faulty, &rdev->flags)) {
		@@ -5549,7 +5554,7 @@ static int raid5_start_reshape(mddev_t *mddev)
		}

		/* When a reshape changes the number of devices, ->degraded
		* is measured against the large of the pre and post number of
		* is measured against the larger of the pre and post number of
		* devices.*/
		if (mddev->delta_disks > 0) {
		spin_lock_irqsave(&conf->device_lock, flags);

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