From 8bce6d35b308d73cdb2ee273c95d711a55be688c Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.com>
Date: Thu, 22 Oct 2015 13:20:15 +1100
Subject: [PATCH] md/raid10: fix the 'new' raid10 layout to work correctly.
In Linux 3.9 we introduce a new 'far' layout for RAID10 which was
supposed to rotate the replicas differently and so provide better
resilience. In particular it could survive more combinations of 2
drive failures.
Unfortunately. due to a coding error, this some did what was wanted,
sometimes improved less than we hoped, and sometimes - in very
unlikely circumstances - put multiple replicas on the same device so
the redundancy was harmed.
No public user-space tool has created arrays using this layout so it
is very unlikely that zero-redundancy arrays actually exist. Probably
no arrays using any form of the new layout exist. But we cannot be
certain.
So use another bit in the 'layout' number and introduce a bug-fixed
version of the layout.
Also when assembling an array, if it has a zero-redundancy layout,
give a warning.
Reported-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/raid10.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 23de2144ee13..96f365968306 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -39,6 +39,7 @@
* far_copies (stored in second byte of layout)
* far_offset (stored in bit 16 of layout )
* use_far_sets (stored in bit 17 of layout )
+ * use_far_sets_bugfixed (stored in bit 18 of layout )
*
* The data to be stored is divided into chunks using chunksize. Each device
* is divided into far_copies sections. In each section, chunks are laid out
@@ -1497,6 +1498,8 @@ static void status(struct seq_file *seq, struct mddev *mddev)
seq_printf(seq, " %d offset-copies", conf->geo.far_copies);
else
seq_printf(seq, " %d far-copies", conf->geo.far_copies);
+ if (conf->geo.far_set_size != conf->geo.raid_disks)
+ seq_printf(seq, " %d devices per set", conf->geo.far_set_size);
}
seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,
conf->geo.raid_disks - mddev->degraded);
@@ -3394,7 +3397,7 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
disks = mddev->raid_disks + mddev->delta_disks;
break;
}
- if (layout >> 18)
+ if (layout >> 19)
return -1;
if (chunk < (PAGE_SIZE >> 9) ||
!is_power_of_2(chunk))
@@ -3406,7 +3409,22 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
geo->near_copies = nc;
geo->far_copies = fc;
geo->far_offset = fo;
- geo->far_set_size = (layout & (1<<17)) ? disks / fc : disks;
+ switch (layout >> 17) {
+ case 0: /* original layout. simple but not always optimal */
+ geo->far_set_size = disks;
+ break;
+ case 1: /* "improved" layout which was buggy. Hopefully no-one is
+ * actually using this, but leave code here just in case.*/
+ geo->far_set_size = disks/fc;
+ WARN(geo->far_set_size < fc,
+ "This RAID10 layout does not provide data safety - please backup and create new array\n");
+ break;
+ case 2: /* "improved" layout fixed to match documentation */
+ geo->far_set_size = fc * nc;
+ break;
+ default: /* Not a valid layout */
+ return -1;
+ }
geo->chunk_mask = chunk - 1;
geo->chunk_shift = ffz(~chunk);
return nc*fc;
--
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