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btrfs-progs: mkfs: enable NO_HOLES by default

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The no-holes feature reduces consumption of metadata by not representing
file holes. Reducing metadata is a good thing in general, this is the
main goal to enable this by default.

There's a drawback, related to the missing information about holes. The
'check' tool cannot use it to cross-reference extent information and in
some cases may not be able to detect a problem.

The no-hole feature can be also enabled by 'btrfstune -n' on an
unmounted filesystem.

Issue: #405
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2021-09-29 15:12:21 +02:00
parent 6d2bf4cbce
commit 1f918def34
3 changed files with 3 additions and 2 deletions
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2
Documentation/mkfs.btrfs.asciidoc
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@ -241,7 +241,7 @@ are selected
reduced-size metadata for extent references, saves a few percent of metadata reduced-size metadata for extent references, saves a few percent of metadata
*no-holes*:: *no-holes*::
(kernel support since 3.14) (default since btrfs-progs 5.15, kernel support since 3.14)
+ +
improved representation of file extents where holes are not explicitly improved representation of file extents where holes are not explicitly
stored as an extent, saves a few percent of metadata if sparse files are used stored as an extent, saves a few percent of metadata if sparse files are used

2
common/fsfeatures.c
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@ -110,7 +110,7 @@ static const struct btrfs_feature mkfs_features[] = {
.sysfs_name = "no_holes", .sysfs_name = "no_holes",
VERSION_TO_STRING2(compat, 3,14), VERSION_TO_STRING2(compat, 3,14),
VERSION_TO_STRING2(safe, 4,0), VERSION_TO_STRING2(safe, 4,0),
VERSION_NULL(default), VERSION_TO_STRING2(default, 5,15),
.desc = "no explicit hole extents for files" .desc = "no explicit hole extents for files"
}, { }, {
.name = "raid1c34", .name = "raid1c34",

1
common/fsfeatures.h
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@ -22,6 +22,7 @@
#define BTRFS_MKFS_DEFAULT_NODE_SIZE SZ_16K #define BTRFS_MKFS_DEFAULT_NODE_SIZE SZ_16K
#define BTRFS_MKFS_DEFAULT_FEATURES \ #define BTRFS_MKFS_DEFAULT_FEATURES \
(BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF \ (BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF \
| BTRFS_FEATURE_INCOMPAT_NO_HOLES \
| BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA) | BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA)
/* /*