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authorMike Snitzer <snitzer@redhat.com>2012-03-28 21:41:28 +0400
committerAlasdair G Kergon <agk@redhat.com>2012-03-28 21:41:28 +0400
commitc4a69ecdb463a901b4645230613961e134e897cd (patch)
treec53e0a569f3d390ea2a97f964225d5383c6401ec /Documentation/device-mapper
parent71fd5ae25d88841c08d5bbea90c0f0a12ca05509 (diff)
downloadlinux-c4a69ecdb463a901b4645230613961e134e897cd.tar.xz
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 'Documentation/device-mapper')
-rw-r--r--Documentation/device-mapper/thin-provisioning.txt8
1 files changed, 5 insertions, 3 deletions
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index da50347c0053..a119fbdd0604 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -75,10 +75,12 @@ less sharing than average you'll need a larger-than-average metadata device.
As a guide, we suggest you calculate the number of bytes to use in the
metadata device as 48 * $data_dev_size / $data_block_size but round it up
-to 2MB if the answer is smaller. The largest size supported is 16GB.
+to 2MB if the answer is smaller. If you're creating large numbers of
+snapshots which are recording large amounts of change, you may find you
+need to increase this.
-If you're creating large numbers of snapshots which are recording large
-amounts of change, you may need find you need to increase this.
+The largest size supported is 16GB: If the device is larger,
+a warning will be issued and the excess space will not be used.
Reloading a pool table
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