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diff --git a/Documentation/device-mapper/zero.rst b/Documentation/device-mapper/zero.rst deleted file mode 100644 index 11fb5cf4597c..000000000000 --- a/Documentation/device-mapper/zero.rst +++ /dev/null @@ -1,37 +0,0 @@ -======= -dm-zero -======= - -Device-Mapper's "zero" target provides a block-device that always returns -zero'd data on reads and silently drops writes. This is similar behavior to -/dev/zero, but as a block-device instead of a character-device. - -Dm-zero has no target-specific parameters. - -One very interesting use of dm-zero is for creating "sparse" devices in -conjunction with dm-snapshot. A sparse device reports a device-size larger -than the amount of actual storage space available for that device. A user can -write data anywhere within the sparse device and read it back like a normal -device. Reads to previously unwritten areas will return a zero'd buffer. When -enough data has been written to fill up the actual storage space, the sparse -device is deactivated. This can be very useful for testing device and -filesystem limitations. - -To create a sparse device, start by creating a dm-zero device that's the -desired size of the sparse device. For this example, we'll assume a 10TB -sparse device:: - - TEN_TERABYTES=`expr 10 \* 1024 \* 1024 \* 1024 \* 2` # 10 TB in sectors - echo "0 $TEN_TERABYTES zero" | dmsetup create zero1 - -Then create a snapshot of the zero device, using any available block-device as -the COW device. The size of the COW device will determine the amount of real -space available to the sparse device. For this example, we'll assume /dev/sdb1 -is an available 10GB partition:: - - echo "0 $TEN_TERABYTES snapshot /dev/mapper/zero1 /dev/sdb1 p 128" | \ - dmsetup create sparse1 - -This will create a 10TB sparse device called /dev/mapper/sparse1 that has -10GB of actual storage space available. If more than 10GB of data is written -to this device, it will start returning I/O errors. |