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AIX逻辑卷的LVCB

作者：OoNiceDream【转载时请务必以超链接形式标明文章原始出处和作者信息】
链接：http://www.dbaroad.me/archives/2009/04/aix_lvcb.html

LVCB(逻辑卷控制块):logical volume control block，保存着逻辑卷的重要信息，在mklv时使用-T O选项可以指定其是否存放于LV的头部：

-T O
For big vg format volume groups, the -T O option indicates that the logical volume control block will not occupy the
first block of the logical volume. Therefore, the space is available for application data. Applications can identify
this type of logical volume with the IOC INFO ioctl. The logical volume has a device subtype of DS_LVZ. A logical
volume created without this option has a device subtype of DS_LV. This option is ignored for old and scalable vg
format volume groups.

加了-T O选项，也就是LVCB不会占用LV的第一个块，DD时也就不需要skip了，此时的LVCB存放于VGDA（卷组描述区）中。

在创建LV时，如果没有使用-T O选项，lslv时也就没有DEVICESUBTYPE这一项：

/dev#lslv ocs_spfile
LOGICAL VOLUME:     ocs_spfile             VOLUME GROUP:   vgocstest
LV IDENTIFIER:      00023cf70000d6000000011fd4df8ad5.13 PERMISSION:     read/write
VG STATE:           active/complete        LV STATE:       closed/syncd
TYPE:               raw                    WRITE VERIFY:   off
MAX LPs:            512                    PP SIZE:        128 megabyte(s)
COPIES:             1                      SCHED POLICY:   striped
LPs:                6                      PPs:            6
STALE PPs:          0                      BB POLICY:      relocatable
INTER-POLICY:       maximum                RELOCATABLE:    no
INTRA-POLICY:       middle                 UPPER BOUND:    3
MOUNT POINT:        N/A                    LABEL:          None
MIRROR WRITE CONSISTENCY: on/ACTIVE
EACH LP COPY ON A SEPARATE PV ?: yes (superstrict)
Serialize IO ?:     NO
STRIPE WIDTH:       3
STRIPE SIZE:        128K

使用-T O选项创建的LV，lslv时就可以找到DEVICESUBTYPE这一项：

/dev#mklv -T O -y'ocs_tbs_test01' -t'raw' '-S128K' vgocstest 4 vpath1 vpath2
ocs_tbs_test01
/dev#
/dev#lslv ocs_tbs_test01
LOGICAL VOLUME:     ocs_tbs_test01         VOLUME GROUP:   vgocstest
LV IDENTIFIER:      00023cf70000d6000000011fd4df8ad5.25 PERMISSION:     read/write
VG STATE:           active/complete        LV STATE:       closed/syncd
TYPE:               raw                    WRITE VERIFY:   off
MAX LPs:            512                    PP SIZE:        128 megabyte(s)
COPIES:             1                      SCHED POLICY:   striped
LPs:                6                      PPs:            6
STALE PPs:          0                      BB POLICY:      relocatable
INTER-POLICY:       maximum                RELOCATABLE:    no
INTRA-POLICY:       middle                 UPPER BOUND:    3
MOUNT POINT:        N/A                    LABEL:          None
MIRROR WRITE CONSISTENCY: on/ACTIVE
EACH LP COPY ON A SEPARATE PV ?: yes (superstrict)
Serialize IO ?:     NO
STRIPE WIDTH:       3
STRIPE SIZE:        128K
DEVICESUBTYPE : DS_LVZ

如果LVCB没有损坏，使用以下命令来查看，就可以看到“AIX LVCB”字样：

/dev#od -c /dev/ocs_tbs_test01 | head
0000000    A   I   X       L   V   C   B  \0  \0   r   a   w  \0  \0  \0
0000020   \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000040   \0  \0  \0  \0  \0  \0  \0  \0  \0  \0   0   0   0   2   3   c
0000060    f   7   0   0   0   0   d   6   0   0   0   0   0   0   0   1
0000100    1   f  \0   o   c   s   _   t   b   s   _   t   e   s   t   0
0000120    1  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000140   \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000200   \0  \0  \0   M   o   n       A   p   r       2   0       1   4
0000220    :   5   3   :   2   8       2   0   0   9  \n  \0  \0  \0  \0

或者：

/dev#getlvcb -TA ocs_tbs_test01
   AIX LVCB
   intrapolicy = m
   copies = 1
   interpolicy = x
   lvid = 00023cf70000d6000000011fd4df8ad5.25
   lvname = ocs_tbs_test01
   label = None
   machine id = 23CF7D600
   number lps = 6
   relocatable = n
   strict = s
   stripe width = 3
   stripe size in exponent = 17
   type = raw
   upperbound = 3
   fs =
   time created  = Mon Apr 20 14:53:28 2009
   time modified = Mon Apr 20 14:53:28 2009

今天从徐大哥这里了解到一个IBM的BUG，有可能导致DS_LVZ类开型的LV的LVCB信息丢失，从而导致数据库无法启动，在这里MARK一下：

/dev$instfix -a -k IY94343
IY94343 Abstract: MKLV -TO ON BIG VOLUME GROUPS FAILS TO PUT SOME LV INFORMAT 

IY94343 Symptom Text:
 The lslv command will fail to show the DEVICESUBTYPE : DS_LVZ
 entry for LVs created as DS_LVZ.
 Some applications depending on the subtype, like Oracle, may
 fail to start.

记得还有一次，SA使用IBM TDMF（Softek Transparent Data Migration Facility）进行数据迁移时，失败好几次，最终发现：老存储用的LV是DS_LV,而新存储使用的LV是DS_LVZ，迁移过去后，数据库无法启动了，这也就是文中开头提到的LVCB存储位置不同引起的。而使用RMAN进行迁移，则不受这一限制。

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