€•ý4      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”Œ=/translations/zh_CN/admin-guide/device-mapper/persistent-data”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$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/zh_TW/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/it_IT/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/ja_JP/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/ko_KR/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒPortuguese (Brazilian)”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/pt_BR/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh–sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ=/translations/sp_SP/admin-guide/device-mapper/persistent-data”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒPersistent data”h]”hŒPersistent data”…””}”(hh¼h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhh·h²hh³ŒW/var/lib/git/docbuild/linux/Documentation/admin-guide/device-mapper/persistent-data.rst”h´Kubh¶)”}”(hhh]”(h»)”}”(hŒIntroduction”h]”hŒIntroduction”…””}”(hhÎh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhhËh²hh³hÊh´KubhŒ	paragraph”“”)”}”(hŒÑThe more-sophisticated device-mapper targets require complex metadata
that is managed in kernel.  In late 2010 we were seeing that various
different targets were rolling their own data structures, for example:”h]”hŒÑThe more-sophisticated device-mapper targets require complex metadata
that is managed in kernel.  In late 2010 we were seeing that various
different targets were rolling their own data structures, for example:”…””}”(hhÞh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KhhËh²hubhŒbullet_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒ*Mikulas Patocka's multisnap implementation”h]”hÝ)”}”(hhõh]”hŒ,Mikulas Patockaâ€™s multisnap implementation”…””}”(hh÷h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´Khhóubah}”(h]”h ]”h"]”h$]”h&]”uh1hñhhîh²hh³hÊh´Nubhò)”}”(hŒ,Heinz Mauelshagen's thin provisioning target”h]”hÝ)”}”(hj  h]”hŒ.Heinz Mauelshagenâ€™s thin provisioning target”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´Khj
  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hñhhîh²hh³hÊh´Nubhò)”}”(hŒ5Another btree-based caching target posted to dm-devel”h]”hÝ)”}”(hj#  h]”hŒ5Another btree-based caching target posted to dm-devel”…””}”(hj%  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´Khj!  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hñhhîh²hh³hÊh´Nubhò)”}”(hŒCAnother multi-snapshot target based on a design of Daniel Phillips
”h]”hÝ)”}”(hŒBAnother multi-snapshot target based on a design of Daniel Phillips”h]”hŒBAnother multi-snapshot target based on a design of Daniel Phillips”…””}”(hj<  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´Khj8  ubah}”(h]”h ]”h"]”h$]”h&]”uh1hñhhîh²hh³hÊh´Nubeh}”(h]”h ]”h"]”h$]”h&]”Œbullet”Œ-”uh1hìh³hÊh´KhhËh²hubhÝ)”}”(hŒeMaintaining these data structures takes a lot of work, so if possible
we'd like to reduce the number.”h]”hŒgMaintaining these data structures takes a lot of work, so if possible
weâ€™d like to reduce the number.”…””}”(hjX  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KhhËh²hubhÝ)”}”(hŒìThe persistent-data library is an attempt to provide a re-usable
framework for people who want to store metadata in device-mapper
targets.  It's currently used by the thin-provisioning target and an
upcoming hierarchical storage target.”h]”hŒîThe persistent-data library is an attempt to provide a re-usable
framework for people who want to store metadata in device-mapper
targets.  Itâ€™s currently used by the thin-provisioning target and an
upcoming hierarchical storage target.”…””}”(hjf  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KhhËh²hubeh}”(h]”Œintroduction”ah ]”h"]”Œintroduction”ah$]”h&]”uh1hµhh·h²hh³hÊh´Kubh¶)”}”(hhh]”(h»)”}”(hŒOverview”h]”hŒOverview”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhj|  h²hh³hÊh´KubhÝ)”}”(hŒfThe main documentation is in the header files which can all be found
under drivers/md/persistent-data.”h]”hŒfThe main documentation is in the header files which can all be found
under drivers/md/persistent-data.”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´Khj|  h²hubh¶)”}”(hhh]”(h»)”}”(hŒThe block manager”h]”hŒThe block manager”…””}”(hjž  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhj›  h²hh³hÊh´K ubhÝ)”}”(hŒdm-block-manager.[hc]”h]”hŒdm-block-manager.[hc]”…””}”(hj¬  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K"hj›  h²hubhÝ)”}”(hŒ·This provides access to the data on disk in fixed sized-blocks.  There
is a read/write locking interface to prevent concurrent accesses, and
keep data that is being used in the cache.”h]”hŒ·This provides access to the data on disk in fixed sized-blocks.  There
is a read/write locking interface to prevent concurrent accesses, and
keep data that is being used in the cache.”…””}”(hjº  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K$hj›  h²hubhÝ)”}”(hŒ=Clients of persistent-data are unlikely to use this directly.”h]”hŒ=Clients of persistent-data are unlikely to use this directly.”…””}”(hjÈ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K(hj›  h²hubeh}”(h]”Œthe-block-manager”ah ]”h"]”Œthe block manager”ah$]”h&]”uh1hµhj|  h²hh³hÊh´K ubh¶)”}”(hhh]”(h»)”}”(hŒThe transaction manager”h]”hŒThe transaction manager”…””}”(hjá  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhjÞ  h²hh³hÊh´K+ubhÝ)”}”(hŒdm-transaction-manager.[hc]”h]”hŒdm-transaction-manager.[hc]”…””}”(hjï  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K-hjÞ  h²hubhÝ)”}”(hXØ  This restricts access to blocks and enforces copy-on-write semantics.
The only way you can get hold of a writable block through the
transaction manager is by shadowing an existing block (ie. doing
copy-on-write) or allocating a fresh one.  Shadowing is elided within
the same transaction so performance is reasonable.  The commit method
ensures that all data is flushed before it writes the superblock.
On power failure your metadata will be as it was when last committed.”h]”hXØ  This restricts access to blocks and enforces copy-on-write semantics.
The only way you can get hold of a writable block through the
transaction manager is by shadowing an existing block (ie. doing
copy-on-write) or allocating a fresh one.  Shadowing is elided within
the same transaction so performance is reasonable.  The commit method
ensures that all data is flushed before it writes the superblock.
On power failure your metadata will be as it was when last committed.”…””}”(hjý  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K/hjÞ  h²hubeh}”(h]”Œthe-transaction-manager”ah ]”h"]”Œthe transaction manager”ah$]”h&]”uh1hµhj|  h²hh³hÊh´K+ubh¶)”}”(hhh]”(h»)”}”(hŒThe Space Maps”h]”hŒThe Space Maps”…””}”(hj  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhj  h²hh³hÊh´K8ubhÝ)”}”(hŒ@dm-space-map.h
dm-space-map-metadata.[hc]
dm-space-map-disk.[hc]”h]”hŒ@dm-space-map.h
dm-space-map-metadata.[hc]
dm-space-map-disk.[hc]”…””}”(hj$  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K:hj  h²hubhÝ)”}”(hXt  On-disk data structures that keep track of reference counts of blocks.
Also acts as the allocator of new blocks.  Currently two
implementations: a simpler one for managing blocks on a different
device (eg. thinly-provisioned data blocks); and one for managing
the metadata space.  The latter is complicated by the need to store
its own data within the space it's managing.”h]”hXv  On-disk data structures that keep track of reference counts of blocks.
Also acts as the allocator of new blocks.  Currently two
implementations: a simpler one for managing blocks on a different
device (eg. thinly-provisioned data blocks); and one for managing
the metadata space.  The latter is complicated by the need to store
its own data within the space itâ€™s managing.”…””}”(hj2  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´K>hj  h²hubeh}”(h]”Œthe-space-maps”ah ]”h"]”Œthe space maps”ah$]”h&]”uh1hµhj|  h²hh³hÊh´K8ubh¶)”}”(hhh]”(h»)”}”(hŒThe data structures”h]”hŒThe data structures”…””}”(hjK  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhjH  h²hh³hÊh´KFubhÝ)”}”(hŒDdm-btree.[hc]
dm-btree-remove.c
dm-btree-spine.c
dm-btree-internal.h”h]”hŒDdm-btree.[hc]
dm-btree-remove.c
dm-btree-spine.c
dm-btree-internal.h”…””}”(hjY  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KHhjH  h²hubhÝ)”}”(hŒ«Currently there is only one data structure, a hierarchical btree.
There are plans to add more.  For example, something with an
array-like interface would see a lot of use.”h]”hŒ«Currently there is only one data structure, a hierarchical btree.
There are plans to add more.  For example, something with an
array-like interface would see a lot of use.”…””}”(hjg  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KMhjH  h²hubhÝ)”}”(hX+  The btree is 'hierarchical' in that you can define it to be composed
of nested btrees, and take multiple keys.  For example, the
thin-provisioning target uses a btree with two levels of nesting.
The first maps a device id to a mapping tree, and that in turn maps a
virtual block to a physical block.”h]”hX/  The btree is â€˜hierarchicalâ€™ in that you can define it to be composed
of nested btrees, and take multiple keys.  For example, the
thin-provisioning target uses a btree with two levels of nesting.
The first maps a device id to a mapping tree, and that in turn maps a
virtual block to a physical block.”…””}”(hju  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KQhjH  h²hubhÝ)”}”(hŒValues stored in the btrees can have arbitrary size.  Keys are always
64bits, although nesting allows you to use multiple keys.”h]”hŒValues stored in the btrees can have arbitrary size.  Keys are always
64bits, although nesting allows you to use multiple keys.”…””}”(hjƒ  h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hÜh³hÊh´KWhjH  h²hubeh}”(h]”Œthe-data-structures”ah ]”h"]”Œthe data structures”ah$]”h&]”uh1hµhj|  h²hh³hÊh´KFubeh}”(h]”Œoverview”ah ]”h"]”Œoverview”ah$]”h&]”uh1hµhh·h²hh³hÊh´Kubeh}”(h]”Œpersistent-data”ah ]”h"]”Œpersistent data”ah$]”h&]”uh1hµhhh²hh³hÊh´Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”hÊuh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(hºNŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jÌ  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”hÊŒ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(j¦  j£  jy  jv  jž  j›  jÛ  jØ  j  j  jE  jB  j–  j“  uŒ	nametypes”}”(j¦  ‰jy  ‰jž  ‰jÛ  ‰j  ‰jE  ‰j–  ‰uh}”(j£  h·jv  hËj›  j|  jØ  j›  j  jÞ  jB  j  j“  jH  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
decoration”Nh²hub.