Automatic Storage Management (ASM) provides a simple way to manage Oracle database files across disk storage. ASM uses disk groups and metadata to distribute data extents across disks for redundancy. Rebalancing operations redistribute extents to maintain even distribution as disks are added or removed, and the estimated time for rebalancing can be found in V$ASM_OPERATION. ASM supports different redundancy levels including external, normal, and high redundancy.

1. Automatic Storage Management

2. Objectives Understand how Oracle database files are stored in ASM Calculate how long ASM rebalance operations will take

3. Agenda ASM Instances ASM Disk Groups Metadata Extent Distribution Rebalancing Redundancy

4. ASM Instances

5. ASM Single Instance Architecture OCSSD Daemon Only Dedicated Storage Oracle Clusterware ASM Instance RDBMS Instance Server

6. ASM Single Instance Background Processes Fixed Area Variable Area ASM Cache Oracle 11.1 PMON SMON CKPT LGWR DBW0 VKTM PSP0 MMAN RBAL GMON X000 DIAG DIA0

7. ASM RAC Architecture Storage Network Private Network Public Network Shared Storage Oracle Clusterware ASM Instance RDBMS Instance Node 1 Oracle Clusterware ASM Instance RDBMS Instance Node 2 Oracle Clusterware ASM Instance RDBMS Instance Node 3 Oracle Clusterware ASM Instance RDBMS Instance Node 4

8. ASM RAC Architecture PROD1 TEST1 CLUSTERWARE +ASM1 PROD2 TEST2 CLUSTERWARE +ASM2 PROD TEST Clusterware ASM Instances RDBMS Instances Database Files

9. ASM RAC Instance Background Processes Fixed Area Variable Area ASM Cache Oracle 11.1 PMON SMON CKPT LGWR DBW0 VKTM PSP0 MMAN RBAL GMON X000 DIAG DIA0 LMON LMS0 LMD0 LCK0 DIAG MARK KATE

10. ASM Disk Groups

11. ASM Disk Groups and Disks Disk Group 1 Disk Group 2 Disk Group 3 Disk 1 Disk 4 Disk 2 Disk 6 Disk 5 Disk 7 Disk 3

12. ASM Disk Groups and Disks Disk Group 1 Disk 1 Disk 4 Disk Group 2 Disk 2 Disk 5 Disk 6 Disk 7 Disk 3 Disk Group 3

13. ASM Disk Groups, Disks and Database Files Disk Group 1 Disk 1 Disk 4 Disk Group 2 Disk 2 Disk 5 Disk 6 Disk 7 Disk 3 Disk Group 3 File 1 File 2 File 3 File 4 File 5 File 5 File 6

14. File Extents versus Allocation Units File Extent Logical unit of ASM file Map to allocation units One to many mapping Allocation Unit Physical unit of ASM disk Oracle 10.2 and below Always 1MB Can be increased using _asm_ausize Oracle 11.1 and above Variable size 1MB, 2MB ,4MB, 8MB, 16MB, 32MB, 64MB

15. X$KFFXP Maps file extents to allocation units Only populated in ASM instance Columns include Column Name Description GROUP_KFFXP Disk Group Number NUMBER_KFFXP File Number COMPOUND_KFFXP Disk Group Number || File Number INCARN_KFFXP Incarnation Number PXN_KFFXP Physical Extent Number (within file) XNUM_KFFXP Logical Extent Number (within file) LXN_KFFXP 0=primary, 1=first mirror, 2=second mirror DISK_KFFXP Disk Number AU_KFFXP Allocation Unit Number (within disk) SIZE_KFFXP Size (# allocation units)

16. ASM Metadata Metadata is stored in first 256 files in ASM disk group Space is initially allocated when disk group is created Can be subsequently extended Metadata allocation units are divided into blocks Each block is 4096 bytes Block size specifed using _asm_blksize Metadata files include File# Description 0 Metadata Header 1 File Directory 2 Disk Directory 3 Active Change Directory 4 Continuing Operations Directory 5 Template Directory 6 Alias Directory 9 Attribute directory (optional) 12 Staleness registry (optional)

17. ASM Metadata Active Change Directory Continuing Operations Directory Template Directory Alias Directory Disk Directory File Directory Partner Status Table Metadata Header Free Space Table Allocation Table Disk Header Metadata Header

18. ASM Metadata Initial Allocation (Single Instance) Active Change Directory Records changes to metadata Used during recovery of instance or operation failures Continuing Operations Directory Maintains state of active operations File# AU Description # AUs 0 0 Disk Header, Free Space Table, Allocation Table 1 1 Partner Status Table 1 1 File Directory 1 2 Disk Directory 1 3 Active Change Directory 42 4 Continuing Operations Directory 2 5 Template Directory 1 6 Alias Directory 1

19. ASM Metadata Block Types Type Description 1 KFBTYP_DISKHEAD 2 KFBTYP_FREESPC 3 KFBTYP_ALLOCTBL 4 KFBTYP_FILEDIR 5 KFBTYP_LISTHEAD 6 KFBTYP_DISKDIR 7 KFBTYP_ACDC 8 KFBTYP_CHNGDIR 9 KFBTYP_CODBGO 10 KFBTYP_TMPLTDIR 11 KFBTYP_ALIASDIR 12 KFBTYP_INDIRECT Type Description 13 KFBTYP_PST_NONE 14 KFBTYP_HASHNODE 15 KFBTYP_COD_RBO 16 KFBTYP_COD_DATA 17 KFBTYP_PST_META 18 KFBTYP_PST_DTA 19 KFBTYP_HBEAT 20 KFBTYP_SR 21 KFBTYP_STALEDIR 22 KFBTYP_VOLUMEDIR 23 KFBTYP_ATTRDIR

20. KFED Utility In Oracle 10.2 and above the kfed utility can be used to inspect and edit the contents of ASM blocks [ oracle@server3 ~]$ $ORACLE_HOME/bin/kfed -h as/mlib ASM Library [asmlib='lib'] aun/um AU number to examine or update [AUNUM=number] aus/z Allocation Unit size in bytes [AUSZ=number] blkn/um Block number to examine or update [BLKNUM=number] blks/z Metadata block size in bytes [BLKSZ=number] ch/ksum Update checksum before each write [CHKSUM=YES/NO] cn/t Count of AUs to process [CNT=number] d/ev ASM device to examine or update [DEV=string] o/p KFED operation type [OP=READ/WRITE/MERGE/NEW/FORM/FIND/STRUCT] p/rovnm Name for provisioning purposes [PROVNM=string] s/eek AU number to seek to [SEEK=number] te/xt File name for translated block text [TEXT=string] ty/pe ASM metadata block type number [TYPE=number] This utility should only be used under the guidance of Oracle Support

21. KFED Utility For example to dump blocks in aliases directory in DISKGROUP1 Find group number SELECT disk_kffxp, au_kffxp FROM x$kffxp WHERE group_kffxp = 1 AND number_kffxp = 6 AND lxn_kffxp = 0; Disk Allocation Unit 0 49 Find disk name SELECT group_number FROM v$asm_diskgroup WHERE name = 'DISKGROUP1'; Alias directory is stored in file number 6 SELECT path FROM v$asm_disk WHERE group_number = 1 AND disk_number = 0; Path /dev/oracleasm/disks/VOL1

22. KFED Utility Example (continued) Allocation unit is 1MB Block size is 4096 Therefore there are 256 blocks per allocation unit Starting block offset = 256 * 49 = 12544 for (( f = 12544 ; f < 12544 + 256 ; f++ )) do kfed op=read blkn=$f dev='/dev/oracleasm/disks/VOL1' > blk${f} done

23. Extent Distribution

24. Extent Distribution Creating a disk group: CREATE DISKGROUP diskgroup1 EXTERNAL REDUNDANCY DISK '/dev/oracleasm/disks/VOL1'; Dropping a disk group: DROP DISKGROUP diskgroup1 INCLUDING CONTENTS

25. Extent Distribution 1 disk Disk 0 Metadata Metadata Data 0 1 2 3 4 5 6 7

26. Extent Distribution 2 disks Disk 0 Disk 1 Metadata Metadata Data 0 2 4 6 8 10 12 14 1 3 5 7 9 11 13 15

27. Extent Distribution 4 disks Disk 0 Disk 1 Disk 2 Disk 3 Metadata Metadata Data 0 4 8 12 16 20 24 28 2 6 10 14 18 22 26 30 1 5 9 13 17 21 25 29 3 7 11 15 19 23 27 31

28. Extent Distribution 1 large disk - 1 small disk Disk 0 Disk 1 Metadata Metadata Data 0 1 3 4 6 7 9 10 2 5 8 11

29. Extent Distribution 1 large disk - 3 small disks Disk 1 Disk 2 Metadata Disk 0 Disk 4 Metadata Data 1 6 11 16 0 3 5 8 10 13 15 18 2 7 12 17 4 9 14 19

30. Extent Distribution 2 large disks - 2 small disks Disk 1 Disk 2 Metadata Disk 0 Disk 4 Metadata Data 3 9 15 21 0 2 6 8 12 14 18 20 1 4 7 10 5 11 17 23 13 16 19 22

31. Rebalancing

32. Extent Distribution Adding a disk: ALTER DISKGROUP diskgroup1 ADD DISK '/dev/oracleasm/disks/VOL2' REBALANCE POWER 0; Dropping a disk: ALTER DISKGROUP diskgroup1 DROP DISK 'DISKGROUP1_0002' REBALANCE POWER 0; Rebalancing a disk group: ALTER DISKGROUP diskgroup1 REBALANCE POWER 1;

33. Rebalancing Adding disks - 1 disks to 2 disks Disk 0 Metadata Data Disk 1 0 1 2 3 4 5 6 7 5 7 0 1 2 3 4 5 6 7 5 7 1 3 1 3 STOP

34. Rebalancing Adding disks - 1 disks to 4 disks Disk 0 Disk 1 Disk 2 Disk 3 Metadata Data 0 1 2 3 4 5 6 7 2 6 1 5 0 4 0 1 2 3 4 5 6 7 1 0 4 5 2 6 STOP

35. Rebalancing Adding disks - 2 disks to 3 disks Disk 0 Disk 1 Disk 2 Metadata Data 1 3 5 7 9 11 13 15 0 2 4 6 8 10 12 14 2 5 8 11 0 1 2 3 4 5 0 3 1 4 14 17 16 17

36. Rebalancing Adding disks - 2 disks to 4 disks Disk 0 Disk 1 Disk 2 Disk 3 Metadata Data 1 3 5 7 9 11 13 15 0 2 4 6 8 10 12 14 1 5 9 13 0 4 8 12 0 1 2 3 4 5 6 7 1 0 4 5 2 6 STOP

37. Rebalancing Dropping disks - 3 disks to 1 disk Disk 0 Disk 1 Disk 2 Metadata Data 0 3 6 1 2 4 5 7 4 5 0 3 1 2 4 5 2 5 1 4 8 7 8 1 2 STOP

38. Rebalancing Moving disks - 2 disks to 2 disks Disk 0 Disk 1 Disk 2 Metadata Data 1 3 5 7 9 11 13 15 4 6 8 10 12 14 10 6 2 0 4 8 0 1 2 3 4 5 6 7 0 4 2 6 STOP 2 0 12 14

39. Rebalancing V$ASM_OPERATION Contains details of ongoing rebalance operations Estimate of remaining time Column Name Data Type GROUP_NUMBER NUMBER OPERATION CHAR(5) STATE VARCHAR2(4) POWER NUMBER ACTUAL NUMBER SOFAR NUMBER EST_WORK NUMBER EST_RATE NUMBER EST_MINUTE NUMBER ERROR_CODE VARCHAR2(44)

40. Rebalancing Power Limit Power limit can be 0 to 11 0 disables rebalance operation 1 to 11 specifies number of ARBn background processes used for rebalance In Oracle 10.2 RBAL manages rebalance operation Each ARBn background process is allocated a range of 128 allocation units to rebalance When complete another range is requested AD lock is taken while an allocation unit is being rebalanced Rebalance operations take much longer than theoretically necessary. Possible reasons include: Locking GES updates with other ASM instances Updates to RDBMS instance

41. Rebalancing Summary EST_MINUTES column of V$ASM_OPERATION is reasonably accurate Allow a few minutes for SAN cache to stabilize Check regularly for changes to estimate ASM rebalance operations do not affect workload Locks are only taken briefly Lock mechanism has changed in Oracle 11.1 SAN cache and I/O performance will be affected In Oracle 10.2 rebalancing is fastest if Other ASM instances are shutdown RDBMS instance is shutdown Estimated completion time will be affected by: Use of SAN cache and I/O by rest of workload Rate of change by applications to blocks in ASM files being rebalanced

42. Redundancy

43. Redundancy ASM Supports three levels of redundancy External Redundancy Implemented externally using storage layer Most common configuration in production Normal Redundancy Two copies of each extent maintained in separate failure groups Used with extended clusters Used occasionally in production e.g. CERN Increases CPU overhead on servers High Redundancy Three copies of each extent maintained in separate failure groups Very rare in production

44. ASM Failure Groups - External Redundancy Disk Group Disk 1 Disk 2 Disk 3

45. ASM Failure Groups - Normal Redundancy Failure Group 1 FailureGroup 2 Disk Group Disk 1 Disk 2 Disk 3 Disk 4 Disk 5 Disk 6

46. ASM Failure Groups - High Redundancy Failure Group 1 Disk Group Failure Group 2 Failure Group 3 Disk 1 Disk 2 Disk 1 Disk 2 Disk 1 Disk 2

47. Normal Redundancy 1 Disk Per Failure Group Disk 0 Disk 1 Primary Secondary Metadata Data Primary Secondary 0 1 0 1 2 3 2 3 10 11 Failure Group 1 8 9 6 7 0 1 2 3 4 5 9 10 7 8 5 6 0 1 2 3 4 11 Failure Group 2

48. Normal Redundancy 2 Disks per Failure Group Disk 0 Disk 1 Disk 2 Disk 3 Failure Group 1 Failure Group 2 Primary Secondary Metadata Data Primary Secondary 0 3 0 1 2 3 1 2 4 7 5 6 4 7 5 6 20 23 16 19 12 15 0 3 4 7 8 11 18 21 14 17 10 13 1 2 5 6 9 22 19 20 15 16 11 12 0 3 4 7 8 23 21 22 17 18 13 14 1 2 5 6 9 10

49. High Redundancy 1 Disk per Failure Group Disk 0 Disk 1 Disk 2 Failure Group 1 Primary Secondary Tertiary Metadata Data Primary Secondary Tertiary 0 0 0 0 Failure Group 2 Failure Group 3 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9

50. References Oracle Automatic Storage Management (Oracle Press) Nitin Vengurlekar Murali Vallath Rich Long What ASM and ZFS Can Do For You Jason Arneil - Nominet A Closer Look Inside Oracle ASM Luca Canali - CERN Implementing ASM Without HW Raid Luca Canali - CERN

51. Thanks !