linux-kernel - [PATCH 4.5 110/128] btrfs: allow balancing to dup with multi-device

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Date:	Sun,  5 Jun 2016 15:24:25 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	"Austin S. Hemmelgarn" <ahferroin7@...il.com>,
	David Sterba <dsterba@...e.com>
Subject: [PATCH 4.5 110/128] btrfs: allow balancing to dup with multi-device

4.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Austin S. Hemmelgarn <ahferroin7@...il.com>

commit 88be159c905a2b4f6d59afa352bef410afb6af02 upstream.

Currently, we don't allow the user to try and rebalance to a dup profile
on a multi-device filesystem.  In most cases, this is a perfectly sensible
restriction as raid1 uses the same amount of space and provides better
protection.

However, when reshaping a multi-device filesystem down to a single device
filesystem, this requires the user to convert metadata and system chunks
to single profile before deleting devices, and then convert again to dup,
which leaves a period of time where metadata integrity is reduced.

This patch removes the single-device-only restriction from converting to
dup profile to remove this potential data integrity reduction.

Signed-off-by: Austin S. Hemmelgarn <ahferroin7@...il.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/volumes.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3699,10 +3699,8 @@ int btrfs_balance(struct btrfs_balance_c
 		num_devices--;
 	}
 	btrfs_dev_replace_unlock(&fs_info->dev_replace);
-	allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE;
-	if (num_devices == 1)
-		allowed |= BTRFS_BLOCK_GROUP_DUP;
-	else if (num_devices > 1)
+	allowed = BTRFS_AVAIL_ALLOC_BIT_SINGLE | BTRFS_BLOCK_GROUP_DUP;
+	if (num_devices > 1)
 		allowed |= (BTRFS_BLOCK_GROUP_RAID0 | BTRFS_BLOCK_GROUP_RAID1);
 	if (num_devices > 2)
 		allowed |= BTRFS_BLOCK_GROUP_RAID5;