【Oracle 12c ASM专题】我的第一个Flex Diskgroup

原文链接：
https://martincarstenbach.wordpress.com/2017/07/06/12-2-new-feature-the-flex-asm-disk-group-part-1/

之前我都是从其他分享者那里了解了12.2的flex diskgroup，但直到现在我都没能亲自探索下它有多cool。我相信它真的非常cool而且很值得拿出来分享下。关于这个特性和下面这些测试，有非常多的东西值得一提，所以我选择把它分解成了多个部分（所以这只是第一部分，不出意外的话可能大概也许maybe下周五更新）。

背景

在GI/ASM之前的版本中，尤其是两者都是用的环境，有一些我想做的操作几乎是不可能轻易完成的。许多磁盘组的属性（例如冗余度等）是对这个磁盘组里所有文件都生效的。例如，你想创建一个normal冗余度的磁盘组给某个数据库，high冗余度的磁盘组给其他库，这时你就必须创建两个用于存放数据的磁盘组。ASM 12.2中，Oracle减少了ASM的限制来提供更好的定制化服务，这一点在12.1中可见一斑。可以看下63 ASM disk groups in 11.2和511 in 12.1，虽然这也允许一些定制化，但还是增加了维护的开销。

12.1中人们可以更细粒度的管理存储而且引入了CDB的概念。在创建PDB时，管理员可以指定pdb_storage_clause子句来对PDB做一些限制，例如：

SQL> create pluggable database pdb1   2   admin user someone identified by somepassword  3    ...  4   storage (maxsize 200G);Pluggable database created.

但是，如果数据库建在了一个high冗余度的磁盘组上，该磁盘组上所有文件都继承这个属性。我无法将一个存放在high冗余度磁盘组上的PDB定义为normal冗余度，至少我在12.1中没意识到如何达到这个效果。

Flex Disk Group

Flex Diak Group允许磁盘组内的更细粒度的管理。你可以强化磁盘组内的配额限制（以数据库为粒度比较靠谱），而且你可以给不同的文件组定义不同的冗余度（即不同的数据库、PDB可以有不同的冗余度）。换句话说就是，你可以在同一个磁盘组里建两个库，数据库1是normal冗余度，数据库2是high冗余度。如果数据库2是一个CDB，你甚至可以以PDB为粒度再去管理一些设置（例如冗余度）。

在我的实验环境中，我创建了一个Flex冗余度的磁盘组。该环境为两节点RAC，Oracle版本为12.2.0.1.170620，操作系统版本为Oracle Linux 7.3 with UEK4。我把这个磁盘组取名为FLEX，下面是它的创建命令：

CREATE DISKGROUP FLEX FLEX REDUNDANCY   DISK 'AFD:FLEX1'  DISK 'AFD:FLEX2'    DISK 'AFD:FLEX3'  DISK 'AFD:FLEX4'   DISK 'AFD:FLEX5'  ATTRIBUTE  'compatible.asm'='12.2.0.1', 'compatible.rdbms'='12.2.0.1', 'compatible.advm'='12.2.0.1', 'au_size'='4M’;

注意这里用了AFD(ASM Filter Driver)，为了我的实验配置的。在安装ASM 12.2时这个特性是默认启用的。看看样例代码，我自己确实也意识到了磁盘组名字取得不是很理想。。。。。。例子中的重点是使用了“FLEX REDUNDANCY”，5个隐式创建的故障组和兼容性设置为了12.2。

这篇文章提到了，Flex Disk Group一般可以容忍两个故障组丢失。但是，容忍两个故障组丢失的前提是该磁盘组至少有5个故障组，如果故障组少于5个，则只允许一个故障组丢失。Flex Disk Group最少需要3个故障组。

如果你现在觉得这个新特性很牛逼，这里有个大大的警告：你必须使用12.2的数据库实例才能使用这个特性。

你可以捕获日志输出（从命令开始到结束），因为在12.2 ASM中当你创建新的磁盘组时，观察下磁盘组创建期间到底发生了啥真的很有意思。如果你对详细的信息并不是很感兴趣，可以直接跳过下面这部分。

SQL> CREATE DISKGROUP FLEX FLEX REDUNDANCY  DISK 'AFD:FLEX1' SIZE 10239M DISK 'AFD:FLEX2' SIZE 10239M DISK 'AFD:FLEX3' SIZE 10239M DISK 'AFD:FLEX4' SIZE 10239M DISK 'AFD:FLEX5' SIZE 10239M ATTRIBUTE 'compatible.asm'='12.2.0.1','compatible.rdbms'='12.2.0.1','compatible.advm'='12.2.0.1','au_size'='4M'NOTE: Assigning number (5,0) to disk (AFD:FLEX1)NOTE: Assigning number (5,1) to disk (AFD:FLEX2)NOTE: Assigning number (5,2) to disk (AFD:FLEX3)NOTE: Assigning number (5,3) to disk (AFD:FLEX4)NOTE: Assigning number (5,4) to disk (AFD:FLEX5)2017-07-03 10:38:53.811000 +01:00NOTE: initializing header (replicated) on grp 5 disk FLEX1NOTE: initializing header (replicated) on grp 5 disk FLEX2NOTE: initializing header (replicated) on grp 5 disk FLEX3NOTE: initializing header (replicated) on grp 5 disk FLEX4NOTE: initializing header (replicated) on grp 5 disk FLEX5NOTE: initializing header on grp 5 disk FLEX1NOTE: initializing header on grp 5 disk FLEX2NOTE: initializing header on grp 5 disk FLEX3NOTE: initializing header on grp 5 disk FLEX4NOTE: initializing header on grp 5 disk FLEX5NOTE: Disk 0 in group 5 is assigned fgnum=1NOTE: Disk 1 in group 5 is assigned fgnum=2NOTE: Disk 2 in group 5 is assigned fgnum=3NOTE: Disk 3 in group 5 is assigned fgnum=4NOTE: Disk 4 in group 5 is assigned fgnum=5GMON updating for reconfiguration, group 5 at 657 for pid 45, osid 25857NOTE: group 5 PST updated.NOTE: initiating PST update: grp = 5GMON updating group 5 at 658 for pid 45, osid 25857NOTE: set version 0 for asmCompat 12.2.0.1.0 for group 5NOTE: group FLEX: initial PST location: disks 0000 0001 0002 0003 0004NOTE: PST update grp = 5 completed successfullyNOTE: cache registered group FLEX 5/0x0A58F009NOTE: cache began mount (first) of group FLEX 5/0x0A58F009NOTE: cache is mounting group FLEX created on 2017/07/03 10:38:52NOTE: cache opening disk 0 of grp 5: FLEX1 label:FLEX1NOTE: cache opening disk 1 of grp 5: FLEX2 label:FLEX2NOTE: cache opening disk 2 of grp 5: FLEX3 label:FLEX3NOTE: cache opening disk 3 of grp 5: FLEX4 label:FLEX4NOTE: cache opening disk 4 of grp 5: FLEX5 label:FLEX5* allocate domain 5, valid ? 0kjbdomatt send to inst 2NOTE: attached to recovery domain 5NOTE: cache creating group 5/0x0A58F009 (FLEX)NOTE: cache mounting group 5/0x0A58F009 (FLEX) succeededNOTE: allocating F1X0 (replicated) on grp 5 disk FLEX1NOTE: allocating F1X0 (replicated) on grp 5 disk FLEX2NOTE: allocating F1X0 (replicated) on grp 5 disk FLEX3NOTE: allocating F1X0 on grp 5 disk FLEX1NOTE: allocating F1X0 on grp 5 disk FLEX2NOTE: allocating F1X0 on grp 5 disk FLEX32017-07-03 10:38:56.621000 +01:00NOTE: Created Used Space Directory for 1 threadsNOTE: Created Virtual Allocation Locator (1 extents) and Table (5 extents) directories for group 5/0x0A58F009 (FLEX)2017-07-03 10:39:00.153000 +01:00NOTE: VAM migration has completed for group 5/0x0A58F009 (FLEX)NOTE: diskgroup must now be re-mounted prior to first useNOTE: cache dismounting (clean) group 5/0x0A58F009 (FLEX)NOTE: messaging CKPT to quiesce pins Unix process pid: 25857, image: oracle@rac122pri1 (TNS V1-V3)2017-07-03 10:39:01.805000 +01:00NOTE: LGWR not being messaged to dismountkjbdomdet send to inst 2detach from dom 5, sending detach message to inst 2freeing rdom 5NOTE: detached from domain 5NOTE: cache dismounted group 5/0x0A58F009 (FLEX)GMON dismounting group 5 at 659 for pid 45, osid 25857GMON dismounting group 5 at 660 for pid 45, osid 25857NOTE: Disk FLEX1 in mode 0x7f marked for de-assignmentNOTE: Disk FLEX2 in mode 0x7f marked for de-assignmentNOTE: Disk FLEX3 in mode 0x7f marked for de-assignmentNOTE: Disk FLEX4 in mode 0x7f marked for de-assignmentNOTE: Disk FLEX5 in mode 0x7f marked for de-assignmentSUCCESS: diskgroup FLEX was createdNOTE: cache deleting context for group FLEX 5/0x0a58f009NOTE: cache registered group FLEX 5/0x4718F00CNOTE: cache began mount (first) of group FLEX 5/0x4718F00CNOTE: Assigning number (5,0) to disk (AFD:FLEX1)NOTE: Assigning number (5,1) to disk (AFD:FLEX2)NOTE: Assigning number (5,2) to disk (AFD:FLEX3)NOTE: Assigning number (5,3) to disk (AFD:FLEX4)NOTE: Assigning number (5,4) to disk (AFD:FLEX5)2017-07-03 10:39:08.161000 +01:00NOTE: GMON heartbeating for grp 5 (FLEX)GMON querying group 5 at 663 for pid 45, osid 25857NOTE: cache is mounting group FLEX created on 2017/07/03 10:38:52NOTE: cache opening disk 0 of grp 5: FLEX1 label:FLEX1NOTE: 07/03/17 10:39:07 FLEX.F1X0 found on disk 0 au 10 fcn 0.0 datfmt 1NOTE: cache opening disk 1 of grp 5: FLEX2 label:FLEX2NOTE: 07/03/17 10:39:07 FLEX.F1X0 found on disk 1 au 10 fcn 0.0 datfmt 1NOTE: cache opening disk 2 of grp 5: FLEX3 label:FLEX3NOTE: 07/03/17 10:39:07 FLEX.F1X0 found on disk 2 au 10 fcn 0.0 datfmt 1NOTE: cache opening disk 3 of grp 5: FLEX4 label:FLEX4NOTE: cache opening disk 4 of grp 5: FLEX5 label:FLEX5NOTE: cache mounting (first) flex redundancy group 5/0x4718F00C (FLEX)* allocate domain 5, valid ? 0kjbdomatt send to inst 2NOTE: attached to recovery domain 5start recovery: pdb 5, passed in flags x4 (domain enable 0)validate pdb 5, flags x4, valid 0, pdb flags x204* validated domain 5, flags = 0x200NOTE: cache recovered group 5 to fcn 0.0NOTE: redo buffer size is 512 blocks (2105344 bytes)NOTE: LGWR attempting to mount thread 1 for diskgroup 5 (FLEX)NOTE: LGWR found thread 1 closed at ABA 0.11262 lock domain=0 inc#=0 instnum=0NOTE: LGWR mounted thread 1 for diskgroup 5 (FLEX)NOTE: setting 11.2 start ABA for group FLEX thread 1 to 2.0NOTE: LGWR opened thread 1 (FLEX) at fcn 0.0 ABA 2.0 lock domain=5 inc#=12 instnum=1 gx.incarn=1192816652 mntstmp=2017/07/03 10:39:08.437000NOTE: cache mounting group 5/0x4718F00C (FLEX) succeededNOTE: cache ending mount (success) of group FLEX number=5 incarn=0x4718f00cNOTE: Instance updated compatible.asm to 12.2.0.1.0 for grp 5 (FLEX).NOTE: Instance updated compatible.asm to 12.2.0.1.0 for grp 5 (FLEX).NOTE: Instance updated compatible.rdbms to 12.2.0.1.0 for grp 5 (FLEX).NOTE: Instance updated compatible.rdbms to 12.2.0.1.0 for grp 5 (FLEX).SUCCESS: diskgroup FLEX was mountedNOTE: diskgroup resource ora.FLEX.dg is onlineSUCCESS: CREATE DISKGROUP FLEX FLEX REDUNDANCY  DISK 'AFD:FLEX1' SIZE 10239M DISK 'AFD:FLEX2' SIZE 10239M DISK 'AFD:FLEX3' SIZE 10239M DISK 'AFD:FLEX4' SIZE 10239M DISK 'AFD:FLEX5' SIZE 10239M ATTRIBUTE 'compatible.asm'='12.2.0.1','compatible.rdbms'='12.2.0.1','compatible.advm'='12.2.0.1','au_size'='4M'2017-07-03 10:39:09.429000 +01:00NOTE: enlarging ACD to 2 threads for group 5/0x4718f00c (FLEX)2017-07-03 10:39:11.438000 +01:00SUCCESS: ACD enlarged for group 5/0x4718f00c (FLEX)NOTE: Physical metadata for diskgroup 5 (FLEX) was replicated.adrci> 

一条命令引发了如此多的活动。。。我检查了磁盘组的属性，它看起来并没有很让我费解的地方。

SQL> select name, value from v$asm_attribute   2   where group_number = 5   3   and name not like 'template%';NAME                           VALUE------------------------------ ------------------------------idp.type                       dynamicidp.boundary                   autodisk_repair_time               3.6hphys_meta_replicated           truefailgroup_repair_time          24.0hthin_provisioned               FALSEpreferred_read.enabled         FALSEsector_size                    512logical_sector_size            512content.type                   datacontent.check                  FALSEau_size                        4194304appliance._partnering_type     GENERICcompatible.asm                 12.2.0.1.0compatible.rdbms               12.2.0.1.0compatible.advm                12.2.0.1.0cell.smart_scan_capable        FALSEcell.sparse_dg                 allnonsparseaccess_control.enabled         FALSEaccess_control.umask           066scrub_async_limit              1scrub_metadata.enabled         FALSE22 rows selected.

我没制定任何故障组，所以隐式的将每块盘做成了一个故障组。

SQL> select name, os_mb, failgroup, path from v$asm_disk where group_number = 5;NAME            OS_MB FAILGROUP                      PATH---------- ---------- ------------------------------ --------------------FLEX1           10239 FLEX1                          AFD:FLEX1FLEX2           10239 FLEX2                          AFD:FLEX2FLEX3           10239 FLEX3                          AFD:FLEX3FLEX4           10239 FLEX4                          AFD:FLEX4FLEX5           10239 FLEX5                          AFD:FLEX5

下面的是我的新磁盘组。你可以看到我把Grid Infrastructure Management Repository (GIMR)单独分了个磁盘组叫+MGMT。此外我有一个磁盘组叫+OCR，我用它存放OCR和voting files。除了两个大家看名字就能猜出来干啥用的磁盘组+DATA和+RECO，还有刚刚新建的+FLEX磁盘组。

[oracle@rac122pri1 ~]$ asmcmd lsdgState    Type    Rebal  Sector  Logical_Sector  Block       AU  Total_MB  Free_MB  Req_mir_free_MB  Usable_file_MB  Offline_disks  Voting_files  NameMOUNTED  EXTERN  N         512             512   4096  4194304     20476    17068                0           17068              0             N  DATA/MOUNTED  FLEX    N         512             512   4096  4194304     51180    50676                0               0              0             N  FLEX/MOUNTED  EXTERN  N         512             512   4096  4194304     40956     6560                0            6560              0             N  MGMT/MOUNTED  NORMAL  N         512             512   4096  4194304     15348    14480             5116            4682              0             Y  OCR/MOUNTED  EXTERN  N         512             512   4096  4194304     15356    15224                0           15224              0             N  RECO/[oracle@rac122pri1 ~]$ 

+FLEX的required_mirror_free_mb和 useable_file_mb值为0并不是bug，因为Flex冗余度的磁盘组就应该是这样。后面我们会使用其他查询方法来确定你的数据库的空间使用情况（下次更新会介绍）。

第一部分总结

Flex ASM Disk Group非常的有趣，而且在你测试Oracle 12.2时这个特性绝对值得关注。我承认12.2依然非常的新，而且我相信在第一个大补丁发布前，谨慎的人不会用它做生产使用。我依然非常好奇如何使用ADF才能改变我与ASM相关的工作方式。它或许和ASMLib有点像，但我还没搞清这个问题。

下一章我会讲一些理解Flex ASM disk group所需要的一些额外的概念。