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authorMike Snitzer <snitzer@redhat.com>2012-03-28 18:41:28 +0100
committerAlasdair G Kergon <agk@redhat.com>2012-03-28 18:41:28 +0100
commitc4a69ecdb463a901b4645230613961e134e897cd (patch)
treec53e0a569f3d390ea2a97f964225d5383c6401ec /drivers/md/dm-thin-metadata.h
parent71fd5ae25d88841c08d5bbea90c0f0a12ca05509 (diff)
downloadlinux-stericsson-c4a69ecdb463a901b4645230613961e134e897cd.tar.gz
dm thin: relax hard limit on the maximum size of a metadata device
The thin metadata format can only make use of a device that is <= THIN_METADATA_MAX_SECTORS (currently 15.9375 GB). Therefore, there is no practical benefit to using a larger device. However, it may be that other factors impose a certain granularity for the space that is allocated to a device (E.g. lvm2 can impose a coarse granularity through the use of large, >= 1 GB, physical extents). Rather than reject a larger metadata device, during thin-pool device construction, switch to allowing it but issue a warning if a device larger than THIN_METADATA_MAX_SECTORS_WARNING (16 GB) is provided. Any space over 15.9375 GB will not be used. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm-thin-metadata.h')
-rw-r--r--drivers/md/dm-thin-metadata.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index 859c16896877..ed4725e67c96 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -11,6 +11,19 @@
#define THIN_METADATA_BLOCK_SIZE 4096
+/*
+ * The metadata device is currently limited in size.
+ *
+ * We have one block of index, which can hold 255 index entries. Each
+ * index entry contains allocation info about 16k metadata blocks.
+ */
+#define THIN_METADATA_MAX_SECTORS (255 * (1 << 14) * (THIN_METADATA_BLOCK_SIZE / (1 << SECTOR_SHIFT)))
+
+/*
+ * A metadata device larger than 16GB triggers a warning.
+ */
+#define THIN_METADATA_MAX_SECTORS_WARNING (16 * (1024 * 1024 * 1024 >> SECTOR_SHIFT))
+
/*----------------------------------------------------------------*/
struct dm_pool_metadata;