€•B      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ2/translations/zh_CN/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ2/translations/zh_TW/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ2/translations/it_IT/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ2/translations/ja_JP/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ2/translations/ko_KR/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ2/translations/sp_SP/admin-guide/device-mapper/zero”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒdm-zero”h]”hŒdm-zero”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒL/var/lib/git/docbuild/linux/Documentation/admin-guide/device-mapper/zero.rst”h KubhŒ	paragraph”“”)”}”(hŒÕDevice-Mapper's "zero" target provides a block-device that always returns
zero'd data on reads and silently drops writes. This is similar behavior to
/dev/zero, but as a block-device instead of a character-device.”h]”hŒÝDevice-Mapperâ€™s â€œzeroâ€ target provides a block-device that always returns
zeroâ€™d data on reads and silently drops writes. This is similar behavior to
/dev/zero, but as a block-device instead of a character-device.”…””}”(hh¹hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒ*Dm-zero has no target-specific parameters.”h]”hŒ*Dm-zero has no target-specific parameters.”…””}”(hhÇhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K	hh£hžhubh¸)”}”(hX%  One very interesting use of dm-zero is for creating "sparse" devices in
conjunction with dm-snapshot. A sparse device reports a device-size larger
than the amount of actual storage space available for that device. A user can
write data anywhere within the sparse device and read it back like a normal
device. Reads to previously unwritten areas will return a zero'd buffer. When
enough data has been written to fill up the actual storage space, the sparse
device is deactivated. This can be very useful for testing device and
filesystem limitations.”h]”hX+  One very interesting use of dm-zero is for creating â€œsparseâ€ devices in
conjunction with dm-snapshot. A sparse device reports a device-size larger
than the amount of actual storage space available for that device. A user can
write data anywhere within the sparse device and read it back like a normal
device. Reads to previously unwritten areas will return a zeroâ€™d buffer. When
enough data has been written to fill up the actual storage space, the sparse
device is deactivated. This can be very useful for testing device and
filesystem limitations.”…””}”(hhÕhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒ¡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::”h]”hŒ¤To create a sparse device, start by creating a dm-zero device thatâ€™s the
desired size of the sparse device. For this example, weâ€™ll assume a 10TB
sparse device:”…””}”(hhãhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhŒliteral_block”“”)”}”(hŒ}TEN_TERABYTES=`expr 10 \* 1024 \* 1024 \* 1024 \* 2`   # 10 TB in sectors
echo "0 $TEN_TERABYTES zero" | dmsetup create zero1”h]”hŒ}TEN_TERABYTES=`expr 10 \* 1024 \* 1024 \* 1024 \* 2`   # 10 TB in sectors
echo "0 $TEN_TERABYTES zero" | dmsetup create zero1”…””}”hhósbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1hñhŸh¶h Khh£hžhubh¸)”}”(hX  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::”h]”hX  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, weâ€™ll assume /dev/sdb1
is an available 10GB partition:”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubhò)”}”(hŒ`echo "0 $TEN_TERABYTES snapshot /dev/mapper/zero1 /dev/sdb1 p 128" | \
   dmsetup create sparse1”h]”hŒ`echo "0 $TEN_TERABYTES snapshot /dev/mapper/zero1 /dev/sdb1 p 128" | \
   dmsetup create sparse1”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1hñhŸh¶h K hh£hžhubh¸)”}”(hŒÊThis 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.”h]”hŒÊThis 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
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