From c4a69ecdb463a901b4645230613961e134e897cd Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Wed, 28 Mar 2012 18:41:28 +0100 Subject: 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 Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin-metadata.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'drivers/md/dm-thin-metadata.h') 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; -- cgit v1.2.3