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List:       linux-lvm
Subject:    [linux-lvm] [PATCH] Fix lvextend spoiling redundancy of mirror LV
From:       "Jun'ichi Nomura" <j-nomura () ce ! jp ! nec ! com>
Date:       2006-08-23 21:52:45
Message-ID: 44ECCE2D.5060002 () ce ! jp ! nec ! com
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Hi,

lvextend doesn't allocate extents appropriately if the LV is mirrored.
Attached patch fixes the problem.
If this looks reasonable, please consider to include in LVM2.

Details of the problem:

Suppose I have 4 PVs with sufficient free space and a 2-sided
mirrored LV with size=4MB, I would expect the following LV
as a result of "lvextend -L+4MB":

# lvs -a -olv_name,seg_size,devices vg4
  LV             SSize Devices
  lv0            8.00M lv0_mimage_0(0),lv0_mimage_1(0)
  [lv0_mimage_0] 8.00M /dev/sda(0)
  [lv0_mimage_1] 8.00M /dev/sdb(0)
  [lv0_mlog]     4.00M /dev/sdc(0)

However, actual result was following:

# lvs -a -olv_name,seg_size,devices vg4
  LV             SSize Devices
  lv0            8.00M lv0_mimage_0(0),lv0_mimage_1(0)
  [lv0_mimage_0] 4.00M /dev/sda(0)
  [lv0_mimage_0] 4.00M /dev/sdd(0)
  [lv0_mimage_1] 4.00M /dev/sdb(0)
  [lv0_mimage_1] 4.00M /dev/sda(1)
  [lv0_mlog]     4.00M /dev/sdc(0)

In this case, failure of a PV (/dev/sda) would break whole LV (lv0),
which is not what we expect from mirrored LV.

The cause of the problem is that _check_contiguous() doesn't care
layered LV and cannot find out contiguousness between PV areas.

Thanks,
-- 
Jun'ichi Nomura, NEC Corporation of America


["fix-lvextend-spoiling-redundancy.patch" (text/x-patch)]

Finding contiguous PV segment for mirrored LV.
Check areas[] boundary in _check_contiguous().

Applicable to LVM2 2.02.09.

Steps to reproduce the problem:
  # pvcreate /dev/sd[abcd]
  # vgcreate vg4 /dev/sd[abcd]
  # lvcreate -l1 -m1 -nlv0 vg4
  # lvchange -an vg4/lv0
  # lvextend -l+1 vg4/lv0
  # lvs -a -olv_name,seg_size,devices vg4

--- LVM2/lib/metadata/lv_manip.c        2006-08-23 04:26:43.000000000 -0400
+++ LVM2.fix/lib/metadata/lv_manip.c    2006-08-23 04:29:37.000000000 -0400
@@ -642,12 +642,24 @@ static int _comp_area(const void *l, con
  */
 static int _check_contiguous(struct lv_segment *prev_lvseg,
 			     struct physical_volume *pv, struct pv_area *pva,
-			     struct pv_area **areas)
+			     struct pv_area **areas, uint32_t areas_size)
 {
 	struct pv_segment *prev_pvseg;
 	uint32_t s;
 
-	for (s = 0; s < prev_lvseg->area_count; s++) {
+	for (s = 0; s < prev_lvseg->area_count && s < areas_size; s++) {
+		if (seg_type(prev_lvseg, s) == AREA_LV) {
+			struct logical_volume *lv;
+			struct lv_segment *lastseg;
+			lv = seg_lv(prev_lvseg, s);
+			lastseg = list_item(list_last(&lv->segments),
+					    struct lv_segment);
+			if (_check_contiguous(lastseg, pv, pva, &areas[s],
+					      areas_size - s))
+				return 1;
+			continue;
+		}
+
 		if (seg_type(prev_lvseg, s) != AREA_PV)
 			continue;	/* FIXME Broken */
 
@@ -752,7 +764,8 @@ static int _find_parallel_space(struct a
 					if (prev_lvseg &&
 					    _check_contiguous(prev_lvseg,
 							      pvm->pv,
-							      pva, areas)) {
+							      pva, areas,
+							      areas_size)) {
 						contiguous_count++;
 						goto next_pv;
 					}



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