Oracle ASM 相关的 视图(V$) 和 数据字典（X$）
ASM由于其高度的封装性，使得我们很难知道窥探其内部的原理。可以通过一下视图和数据字典来来查看ASM 的信息。一. 相关视图和数据字典
View Name
X$ Table name
Description
V$ASM_DISKGROUP
X$KFGRP
performs disk discovery and listsdiskgroups
V$ASM_DISKGROUP_STAT
X$KFGRP_STAT
diskgroup stats without disk discovery
V$ASM_DISK
X$KFDSK, X$KFKID
performs disk discovery, lists disks andtheir usage metrics
V$ASM_DISK_STAT
X$KFDSK_STAT, X$KFKID
lists disks and their usage metrics
V$ASM_FILE
X$KFFIL
lists ASM files, includingmetadata/asmdisk files
V$ASM_ALIAS
X$KFALS
lists ASM aliases, files and directories
V$ASM_TEMPLATE
X$KFTMTA
lists the available templates and theirproperties
V$ASM_CLIENT
X$KFNCL
lists DB instances connected to ASM
V$ASM_OPERATION
X$KFGMG
lists rebalancing operations
N.A.
X$KFKLIB
available libraries, includes asmlib path
N.A.
X$KFDPARTNER
lists disk-to-partner relationships
N.A.
X$KFFXP
extent map table for all ASM files
N.A.
X$KFDAT
extent list for all ASM disks
N.A.
X$KFBH
describes the ASM cache (buffer cache ofASM in blocks of 4K (_asm_blksize)
N.A.
X$KFCCE
a linked list of ASM blocks. to befurther investigated
This list is obtained querying v$fixed_view_definitionwhere view_name like '%ASM%' which exposes all the v$ and gv$ views with theirdefinition. Fixed tables are exposed by querying v$fixed_table where name like'x$kf%' (ASM fixed tables use the 'X$KF' prefix).
SQL>select * fromv$fixed_view_definition whereview_name like '%ASM%';
SQL>select * from sys.v$fixed_tablewhere name like 'X$KF%' ;
Noteon 11g there are additional V$views: , and X$tables: *
New in 11g:
View Name
X$ Table name
Description
V$ASM_ATTRIBUTE
X$KFENV
ASM attributes, the X$ table shows also'hidden' attributes
V$ASM_DISK_IOSTAT
X$KFNSDSKIOST
I/O statistics
N.A.
X$KFDFS
N.A.
X$KFDDD
N.A.
X$KFGBRB
N.A.
X$KFMDGRP
N.A.
X$KFCLLE
N.A.
X$KFVOL
N.A.
X$KFVOLSTAT
N.A.
X$KFVOFS
N.A.
X$KFVOFSV
二. Striping and Mirroring with ASM, extentsand allocation units
Abasic example, using ASM and normal redundancy: the available storage, say 64HDs over FC SAN, are used to create the main DB diskgroup: DATADG. DATADG islogically divided into 2 evenly sized groups of disks: 32 disks in failgroupN.1 and 32 in failgroup N.2. Oracle datafiles created in DATADG are 'striped'into smaller pieces, extents of 1MB in size. Extents are allocated to thestorage in 2 (mirrored) allocation units (AU): one AU in failgroup N.1 theother in failgroup N.2.
Allocation Units
EveryASM disk is divided into allocation units (AU). An AU is the fundamental unitof allocation within a disk group. A file extent consists of one or more AU. AnASM file consists of one or more file extents.
When you create a disk group, youcan set the ASM AU size to be between 1 MB and 64 MB in powers of two, such as,1, 2, 4, 8, 16, 32, or 64. Larger AU sizes typically provide performanceadvantages for data warehouse applications that use large sequential reads.
默认的AU 大小是1M。
三. X$KFFXP
ThisX$ table contains the mapping between files, extents and allocation units. Itallows to track the position of all the extents of a given file striped andmirrored across storage.
Note:RDBMS read operations access only the primary extent of a mirrored couple(unless there is an IO error) . Write operations instead write all mirroredextents to disk.
X$KFFXP Column Name
Description
ADDR
x$ table address/identifier
INDX
row unique identifier
INST_ID
instance number (RAC)
NUMBER_KFFXP
ASM file number. Join with v$asm_file andv$asm_alias
COMPOUND_KFFXP
File identifier. Join with compound_indexin v$asm_file
INCARN_KFFXP
File incarnation id. Join withincarnation in v$asm_file
PXN_KFFXP
Progressive file extent number
XNUM_KFFXP
ASM file extent number (mirrored extentpairs have the same extent value)
GROUP_KFFXP
ASM disk group number. Join withv$asm_disk and v$asm_diskgroup
DISK_KFFXP
Disk number where the extent isallocated. Join with v$asm_disk
AU_KFFXP
Relative position of the allocation unitfrom the beginning of the disk. The allocation unit size (1 MB) inv$asm_diskgroup
LXN_KFFXP
0->primary extent, ->mirror extent,2->2nd mirror copy (high redundancy and metadata)
FLAGS_KFFXP
N.K.
CHK_KFFXP
N.K.
SIZE_KFFXP
11g, to support variable size AU, integervalue which marks the size of the extent in AU size units.
Example1 - reading ASM files with direct OS access
（1）Find the 2 mirrored extents of an ASM file (thespfile in this example)
sys@+ASM1>selectGROUP_KFFXP,DISK_KFFXP,AU_KFFXP from x$kffxp where number_kffxp=(selectfile_number from v$asm_alias where name='spfiletest1.ora');
GROUP_KFFXP DISK_KFFXP AU_KFFXP
----------- ---------- ----------
1 20 379
1 3 101
（2）find the diskname
sys@+ASM1> select disk_number,path fromv$asm_disk where GROUP_NUMBER=1 anddisk_number in (3,20);
DISK_NUMBER PATH
---------------------------------------------------
3 /dev/mpath/itstor417_2p1
20 /dev/mpath/itstor419_2p1
（3）access the data directly from disk with dd
ddif=/dev/mpath/itstor417_2p1 bs=1024k count=1 skip=101|strings|more
四. X$KFDAT
This X$ table contains details of all allocation units (free and used).
X$KFDAT Column Name
Description
ADDR
x$ table address/identifier
INDX
row unique identifier
INST_ID
instance number (RAC)
GROUP_KFDAT
diskgroup number, join withv$asm_diskgroup
NUMBER_KFDAT
disk number, join with v$asm_disk
COMPOUND_KFDAT
disk compund_index, join with v$asm_disk
AUNUM_KFDAT
Disk allocation unit (relative positionfrom the beginning of the disk), join with x$kffxp.au_kffxp
V_KFDAT
V=this Allocation Unit is used; F=AU isfree
FNUM_KFDAT
file number, join with v$asm_file
I_KFDAT
N.K.
XNUM_KFDAT
Progressive file extent number join withx$kffxp.pxn_kffxp
RAW_KFDAT
raw format encoding of the disk,and fileextent information
Example2 - listallocation units of a given file from x$kfdat
similarly to example 1 above, another wayto retrieve ASM file allocation maps:
sys@+ASM1> selectGROUP_KFDAT,NUMBER_KFDAT,AUNUM_KFDAT from x$kfdat where fnum_kfdat=(selectfile_number from v$asm_alias where name='spfiletest1.ora');
GROUP_KFDAT NUMBER_KFDAT AUNUM_KFDAT
----------- ------------ -----------
1 3 101
1 20 379
Example3 - from strace data of an oracle userprocess
（1）from the strace file of a user(shadow) process identify IO operations:
ex: strace-p 30094 2>&1|grep -v time
read64(15,"#\242\0\0\33\0@\2\343\332\177\303s\5\1\4\211\330\0\0\0"..., 8192,473128960) = 8192
itis a read operation of 8KB (oracle block) at the offset 473128960 (=451 MB +27*8KB) from file descriptor FD=15
（2）using /proc/30094/fd -> findFD=15 is /dev/mpath/itstor420_1p1
（3）I find the group and disk number ofthe file:
sys@+ASM1> selectGROUP_NUMBER,DISK_NUMBER from v$asm_disk
where path='/dev/mpath/itstor420_1p1';
GROUP_NUMBER DISK_NUMBER
------------ -----------
1 30
（4）using the disk number, group numberand offset (from strace above) I find the file number and extent number:
sys@+ASM1> select number_kffxp,XNUM_KFFXP from x$kffxp where group_kffxp=1 and disk_kffxp=20 and au_kffxp=451;
NUMBER_KFFXP XNUM_KFFXP
------------ ----------
268 17
（5）from v$asm_file fnum=268 is file ofthe users' tablesspace:
sys@+ASM1> select name from v$asm_aliaswhere FILE_NUMBER=268
NAME
------------------------------
USERS.268.612033477
sys@DB> select file#,name fromv$datafile where upper(name) like '%USERS.268.612033477';
FILE# NAME
------------------------------------------------------------------
9 +TEST1_DATADG1/test1/datafile/users.268.612033477
（6）from dba extents finally find theowner and segment name relative to the original IO operation:
sys@TEST1> selectowner,segment_name,segment_type from dba_extents
where FILE_ID=9 and 27+17*1024*1024 betweenblock_id and block_id+blocks;
OWNER SEGMENT_NAME SEGMENT_TYPE
------------------------------------------------------------ ------------------
SCOTT EMP TABLE
五. X$KFDPARTNER
ThisX$ table contains the disk-to-partner (1-N) relationship. Two disks of a givenASM diskgroup are partners if they each contain a mirror copy of the sameextent. Therefore partners must belong to different failgroups of the samediskgroup. From a few liveexamples I can see that typically disks have 10 partners each atdiskgroup creation and fluctuate around 10 partners following ASM operations.This mechanism is in place to reduce the chance of losing both sides of themirror in case of double disk failure.
X$KFDPARTNER Column Name
Description
ADDR
x$ table address/identifier
INDX
row unique identifier
INST_ID
instance number (RAC)
GRP
diskgroup number, join withv$asm_diskgroup
DISK
disk number, join with v$asm_disk
COMPOUND
disk identifier. Join with compound_indexin v$asm_disk
NUMBER_KFDPARTNER
partner disk number, i.e. disk-to-partner(1-N) relationship
MIRROR_KFDPARNER
=1 in a healthy normal redundancy config
PARITY_KFDPARNER
=1 in a healthy normal redundancy config
ACTIVE_KFDPARNER
=1 in a healthy normal redundancy config
六. X$KFFIL and metadata files
Three types of metadata:
（1）diskgroup metadata: files with NUMBER_KFFIL <256 ASM metadata andASMlog files. These files have high redundancy (3 copies) and block size =4KB.
1）ASM log files are used for ASMinstance and crash recovery when a crash happens with metadata operations (seebelow COD and ACD)
2）at diskgroup creation 6 files withmetadata are visible from x$kffil
（2）disk metadata: disk headers (typically the first 2 AU of each disk)are not listed in x$kffil (they appear as file number 0 in x$kfdat). Containdisk membership information. This part of the disk has to be 'zeroed out'before the disk can be added to ASM diskgroup as a new disk.
（3）file metadata: 3 mirrored extents with file metadata, visible fromx$kffxp and x$kfdat
Example: list all files,system and users' with their sizes:
SYS@+ASM2(rac2)> select group_kffil group#,number_kffil file#, filsiz_kffil filesize_after_mirr, filspc_kffilraw_file_size from x$kffil;
GROUP# FILE# FILESIZE_AFTER_MIRRRAW_FILE_SIZE
---------- ---------- --------------------------------
1 1 2097152 2097152
1 2 1048576 1048576
1 3 88080384 89128960
1 4 1392640 2097152
1 5 1048576 1048576
1 6 1048576 1048576
1 256 545267712 547356672
1 257 629153792 631242752
1 258 351281152 353370112
1 259 7872512 8388608
1 260 15319040 16777216
Example: List all filesincluding metadata allocated in the ASM diskgroups
SYS@+ASM2(rac2)> select group_kfdat group#,FNUM_KFDAT file#, sum(1) AU_used from x$kfdat where v_kfdat='V' group by group_kfdat,FNUM_KFDAT,v_kfdat;
GROUP# FILE# AU_USED
---------- ---------- ----------
1 0 2
1 1 2
1 2 1
1 3 85
1 4 2
1 5 1
1 6 1
1 256 522
1 257 602
1 258 337
1 259 8
Descriptionof metadata files
This paragraph is from: Oracle AutomaticStorage Management, Oracle Press Nov 2007, N. Vengurlekar, M. Vallath, R.Long
（1）. File#0, AU=0: disk header (disk name, etc), Allocation Table (AT)and Free Space Table (FST)
（2）. File#0, AU=1: Partner Status Table (PST)
（3）. File#1: File Directory (files and their extent pointers)
（4）. File#2: Disk Directory
（5）. File#3: Active Change Directory (ACD) The ACD is analogous to a redolog, where changes to the metadata are logged. Size=42MB * number of instances
（6）. File#4: Continuing Operation Directory (COD). The COD is analogousto an undo tablespace. It maintains the state of active ASM operations such asdisk or datafile drop/add. The COD log record is either committed or rolledback based on the success of the operation.
（7）. File#5: Template directory
（8）. File#6: Alias directory
（9）. 11g, File#9: Attribute Directory
（10）. 11g, File#12: Stalenessregistry, created when needed to track offline disks
七. DBMS_DISKGROUP, an internal ASM package
dbms_diskgroupis an Oracle 'internal package' (it doesn't show up as an object being that ASMhas no dictionary) called dbms_diskgroup. It is used to access the ASM withfilesystem-like calls. 11g asmcmd uses this package to implement the cpcommand. A list of procedures:
dbms_diskgroup.open(:fileName, :openMode,:fileType, :blkSz, :hdl,:plkSz, :fileSz)
dbms_diskgroup.createfile(:fileName,:fileType, :blkSz, :fileSz, :hdl, :plkSz, :fileGenName)
dbms_diskgroup.close(:hdl)
dbms_diskgroup.read(:hdl, :offset,:blkSz, :data_buf)
dbms_diskgroup.commitfile(:handle)
dbms_diskgroup.resizefile(:handle,:fsz)
dbms_diskgroup.remap(:gnum, :fnum,:virt_extent_num)
dbms_diskgroup.getfileattr(:fileName,:fileType, :fileSz, :blkSz)
dbms_diskgroup.checkfile(?)
dbms_diskgroup.patchfile(?)
八. ASM parameters and underscore parameters
可以使用SQL 查看ASM 参数：
/* Formatted on 2011/8/30 16:28:54(QP5 v5.163.1008.3004) */
SELECT a.ksppinm"Parameter", c.ksppstvl"Instance Value"
FROMx$ksppi a,x$ksppcv b,x$ksppsv c
WHERE a.indx = b.indx AND a.indx = c.indx ANDksppinm LIKE '%asm%'
ORDER BY a.ksppinm;
或者：
select * fromall_parameters where name like '%asm%';
Parameter Name
Value
_asm_acd_chunks
1
_asm_allow_only_raw_disks
TRUE
_asm_allow_resilver_corruption
FALSE
_asm_ausize
1048576
_asm_blksize
4096
_asm_disk_repair_time
14400
_asm_droptimeout
60
_asm_emulmax
10000
_asm_emultimeout
0
_asm_kfdpevent
0
_asm_libraries
ufs (may differ if asmlib is used)
_asm_maxio
1048576
_asm_stripesize
131072
_asm_stripewidth
8
_asm_wait_time
18
_asmlib_test
0
_asmsid
asm
asm_diskgroups
list of diskgroups to be mounted at startup
asm_diskstring
search path for physical disks to be usedwith ASM
asm_power_limit
default rebalance power value
注意这里的_asm_ausize =1M
Oracle 11g 里新增加的参数：
Parameter Name
Value
_asm_compatibility
10.1
_asm_dbmsdg_nohdrchk
FALSE
_asm_droptimeout
removed in 11g
_asm_kfioevent
0
_asm_repairquantum
60
_asm_runtime_capability_volume_support
FALSE
_asm_skip_resize_check
FALSE
_lm_asm_enq_hashing
TRUE
asm_preferred_read_failure_groups
九. ASM-related acronyms 相关名词解释
（1）. PST - Partner Status Table. Maintains info on disk-to-diskgroupmembership.
（2）. COD - Continuing Operation Directory. The COD structuremaintains the state of active ASM operations or changes, such as disk ordatafile drop/add. The COD log record is either committed or rolled back basedon the success of the operation. (source Oracle whitepaper)
（3）. ACD - Active Change Directory. The ACD is analogous to a redolog, where changes to the metadata are logged. The ACD log record is used todetermine point of recovery in the case of ASM operation failures or instancefailures. (source Oracle whitepaper)
（4）. OSM Oracle Storage Manager, legacy name, synonymous of ASM
（5）. CSS Cluster Synchronization Services. Part of Oracleclusterware, mandatory with ASM even in single instance. CSS is used toheartbeat the health of the ASM instances.
（6）. RBAL - Oracle backgroud process. In an ASM instance coordinatedrebalancing operations. In a DB instance, opens and mount diskgroups from thelocal ASM instance.
（7）. ARBx - Oracle backgroud processes. In an ASM instance, a slavefor rebalancing operations
（8）. PSPx - Oracle backgroud processes. In an ASM instance, ProcessSpawners
（9）. GMON - Oracle backgroud processes. In an ASM instance,diskgroup monitor.
（10）. ASMB - Oracle backgroudprocess. In an DB instance, keeps a (bequeath) persistent DB connection to thelocal ASM instance. Provides hearthbeat and ASM statistics. During a diskgrouprebalancing operation ASM communicates to the DB AU changes via this connection.
（11）. O00x - Oracle backgroudprocesses. Slaves used to connected from the DB to the ASM instance for 'shortoperations'.
https://blog.51cto.com/u_15462270/4868291
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