As Published In
Oracle Magazine
March/April 2006

TECHNOLOGY: ASM


Commanding ASM

By Arup Nanda Oracle ACE Director

Access, transfer, and administer ASM files without SQL commands.

Oracle Database 10g Release 1 introduced Automatic Storage Management (ASM), a new framework for managing Oracle database files. ASM provided a foundation for highly efficient storage management with kernelized asynchronous I/O, direct I/O, redundancy, striping, and an easy way to manage storage. ASM includes volume management functionality similar to that of a generic logical volume manager (LVM).

Managing ASM through SQL interfaces in Oracle Database 10g Release 1 posed a challenge for system administrators who were not very familiar with SQL and preferred a more conventional command-line interface. In Oracle Database 10g Release 2, you have an option to manage the ASM files by using ASMCMD—a powerful and easy-to-use command-line tool.

In Oracle Database 10g Release 1, ASM disk groups are not visible outside the database for regular file system administration tasks such as copying and creating directories. In Oracle Database 10g Release 2, however, you can transfer the files from ASM to locations outside of the disk groups via FTP and through a Web browser using HTTP.

This article shows you how to use these enhancements in ASM to accomplish everyday tasks.

Command-Line Tool

ASMCMD is included in the installation of the Oracle Database 10g Release 2 software; no setup is necessary.

To use ASMCMD, first set the ORACLE_SID to the correct ASM instance. Typically it's named +ASM: 

export ORACLE_SID=+ASM


From the OS command prompt, type asmcmd , which brings up the ASM command-line prompt: 

ASMCMD>


Common Commands

You can invoke the ASMCMD tool with a -p parameter to always display the present directory inside the prompt itself. Once at the prompt, use the cd command to go to a particular directory. To check which directories and files are available inside a directory, use the ls command. Let's see it in action: 

$ asmcmd -p
ASMCMD [+] > ls 
USERDG1/
USERDG2/
USERDG3/
USERDG4/
USERDG5/
ASMCMD [+] > cd USERDG1
ASMCMD [+USERDG1] >


Note how the prompt changed; it now shows the current directory (USERDG1).

When you want to create a directory, use the mkdir command as follows: 

ASMCMD [+USERDG1] > mkdir test


To remove a directory, use the rm command, which removes both files and directories.

Advanced Commands

To display the details of the files and directories, rather than simple names, use the -l parameter with the ls command. Listing 1 presents a sample ls -l command and result. Let's look at the output.

Listing 1: The -l modifier to ls 

                               
ASMCMD [+USERDG2/DBA102] > ls -l
Type Redund Striped Time  Sys  Name
                          Y    CONTROLFILE/
                          Y    DATAFILE/
                          Y    ONLINELOG/
                          Y    TEMPFILE/
                          N    control01.ctl => +USERDG2/DBA102/CONTROLFILE/Current.260.573852215
                          N    control02.ctl => +USERDG2/DBA102/CONTROLFILE/Current.261.573852215
                          N    control03.ctl => +USERDG2/DBA102/CONTROLFILE/Current.262.573852215
                          N    example01.dbf => +USERDG2/DBA102/DATAFILE/UNKNOWN.267.573852295
                          N    redo01.log => +USERDG2/DBA102/ONLINELOG/group_1.263.573852243
                          N    redo02.log => +USERDG2/DBA102/ONLINELOG/group_2.264.573852249
                          N    redo03.log => +USERDG2/DBA102/ONLINELOG/group_3.265.573852255
                          N    sysaux01.dbf => +USERDG2/DBA102/DATAFILE/SYSAUX.257.573852115
                          N    system01.dbf => +USERDG2/DBA102/DATAFILE/SYSTEM.256.573852113
                          N    temp01.dbf => +USERDG2/DBA102/TEMPFILE/TEMP.266.573852277
                          N    undotbs01.dbf => +USERDG2/DBA102/DATAFILE/UNDOTBS1.258.573852115
                          N    users01.dbf => +USERDG2

                            


In Listing 1, the last column—Name—shows the name of the file or the directory. Both the real names and the aliases are reported. For instance, in the output in Listing 1, the alias control01.ctl refers to the real ASM file +USERDG2/DBA102/CONTROLFILE/Current.260.573852215.

The Sys column—immediately to the left of the Name column—shows if the file or directory was created by the ASM system. In the Listing 1 output, for instance, the CONTROLFILE directory was created by SYSTEM, so the Sys flag is Y. This directory was created when the database was created.

Because the CONTROLFILE directory is not a real file but an alias, the attributes of the alias—such as size, free space, and redundancy—shown in the first few columns of the output are null.

If you use the same ls -l command for the actual file—+USERDG2/DBA102/CONTROLFILE/Current.260.573852215—as you did for the alias, you will get the attributes in the output. To see file space usage information, use the -ls option with the ls command, as shown in Listing 2 . Let's look at the output of Listing 2 .

The Type column indicates the type of the file. In this example, the type of all three files is CONTROLFILE. Depending on the type of the file, the values in this column can be any of the following: 

  • CONTROLFILE
  • DATAFILE
  • ONLINELOG
  • ARCHIVELOG
  • TEMPFILE
  • BACKUPSET
  • XTRANSPORT
  • PARAMETERFILE
  • DATAGUARDCONFIG
  • FLASHBACK
  • CHANGETRACKING
  • DUMPSET
  • AUTOBACKUP


Each file is in a disk group that is on only one physical disk, so the Redund column in Listing 2 shows UNPROT (for unprotected ). (Note that the disk group might be mirrored at the hardware level, which ASM is not aware of. In such a case, ASM still reports it as unprotected.) The files in Listing 2 are control files, and they are striped finely by ASM, hence the Striped column shows FINE. The Time column shows when each file was created. The Sys column for each file shows Y, indicating that the control files were created by the ASM system, not by the user. The Blocks and Block_Size columns in Listing 2 show the number of blocks and the size of each block in bytes in each file, respectively. The total file size in bytes is shown in the Bytes column. The actual space allocated to each file may be more than the actual size of the file and is shown in bytes in the Space column.

To find out how much space is used in a directory, you can issue the du command, as follows: 

ASMCMD [+USERDG1] > du . 
Used_MB      Mirror_used_MB
     14                  14


The total space used in the directory is shown in the Used_MB column. If the disk group has been mirrored, the mirrored space is shown in the Mirror_used_MB column. In this case, they are the same, because the disk groups are not mirrored.

To find out about the disk groups in the ASM storage, you can use the lsdg command, as shown in Listing 3. The name of the disk group is the last column, Name. The Type column shows the type of redundancy of the disk group. In Listing 3, the Type column shows EXTERN for all groups, because the groups were created as externally mirrored. The State column shows the status of the disks—MOUNTED, DISMOUNTED, and so on. If the ASM disk group needs rebalancing, the Unbal column shows Y.

The total space available in the disk group is shown in the Total_MB column in Listing 3, and the unused capacity is shown in the Free_MB column. If I had used ASM mirroring instead of hardware-level external mirroring, some space would have been required for the mirroring. This space is shown in the Req_mir_free_MB column. The value of the Usable_file_MB column shows the file space available, and the value is the same as the result of Free_MB - Req_mir_free_MB.

An ASM instance serves as a storage container; it's not a database by itself. Other databases use the space in the ASM instance for datafiles, control files, and so on. How do you know how many databases are using an ASM instance? A simple lsct command will show you that information. Listing 4 shows the lsct command and output. The names of the databases using this ASM instance are shown in the DB_Name column.

Code Listing 4: Displaying the real ASM file attributes 

                               
ASMCMD [+USERDG1] > lsct
DB_Name         Status           Software_Version       Compatible_version      Instance_Name
DBA102          CONNECTED        10.2.0.1.0             10.2.0.1.0              DBA102
EMREP           CONNECTED        10.2.0.1.0             10.2.0.1.0              EMREP

                            


FTP and HTTP Access

Because ASM is not a regular file system, you can't use the standard FTP and HTTP services to access these files. To access them, you can use the file mapping functionalities provided by the Oracle XML Database (Oracle XML DB) feature. This section shows you how to set up FTP and HTTP to access the ASM files and transfer them as regular OS files. This access requires a one-time setup.

Setup. FTP and HTTP services are mapped to a port on the server. By default, the FTP and HTTP services run on ports 21 and 80, respectively. However, ASM FTP and HTTP do not use the default services; they use the specialized services provided by Oracle XML DB. You have to use two different ports—one for FTP and the other for HTTP services. Typically, Oracle users choose 7777 for FTP and 8080 for HTTP, but you are free to choose any unused port number. For my setup, I want to use 8080 for HTTP and 7787 for FTP. I use the 7787 port deliberately, to show how different port numbers can be used.

To set up the FTP access, I must first set up the Oracle XML DB access to the ASM folders. I can do this by executing the catxdbdbca.sql script, found in the $ORACLE_HOME/rdbms/admin directory. The script takes two parameters: the port numbers for the FTP and HTTP services, respectively. So I run the script as follows: 

@catxdbdbca 7787 8080


Running the script enables an FTP service listening on port 7787 and an HTTP service on port 8080. I can access the ASM folders from an external source, using a regular FTP client (such as ftp.exe, provided in Windows). Listing 5 shows a sample FTP session on a Windows system accessing ASM folders. To clarify the explanation, I have prefixed each line with a line number; the line numbers do not appear in the actual output.

Code Listing 5: FTP interaction with ASM files 

1. C:\WUTemp>ftp
2. ftp> open prolin1 7787
3. Connected to prolin1.
4. 220- prolin1
5. Unauthorized use of this FTP server is 
                prohibited and may be subject to civil and 
                criminal prosecution.
6. 220 prolin1 FTP Server (Oracle XML DB/Oracle 
      Database) ready.
7. User (prolin1:(none)): system
8. 331 pass required for SYSTEM
9. Password:
10. 230 SYSTEM logged in
11. ftp> cd /sys/asm
12. 250 CWD Command successful
13. ftp> ls
14. 200 PORT Command successful
15. 150 ASCII Data Connection
16. USERDG5
17. USERDG4
18. USERDG3
19. USERDG2
20. USERDG1
21. 226 ASCII Transfer Complete
22. ftp: 45 bytes received in 0.26Seconds 
         0.17Kbytes/sec.
23. ftp> cd USERDG2
24. 250 CWD Command successful
25. ftp> ls
26. 200 PORT Command successful
27. 150 ASCII Data Connection
28. emrep
29. DBA102
30. 226 ASCII Transfer Complete
31. ftp: 15 bytes received in 0.01Seconds 
         1.50Kbytes/sec.
32. ftp> cd DBA102
33. 250 CWD Command successful
34. ftp> ls
35. 200 PORT Command successful
36. 150 ASCII Data Connection
37. DATAFILE
38. system01.dbf
39. sysaux01.dbf
40. undotbs01.dbf
41. users01.dbf
42. CONTROLFILE
43. control01.ctl
44. control02.ctl
45. control03.ctl
46. ONLINELOG
47. redo01.log
48. redo02.log
49. redo03.log
50. TEMPFILE
51. temp01.dbf
52. example01.dbf
53. 226 ASCII Transfer Complete
54. ftp: 208 bytes received in 0.02Seconds 
10. 40Kbytes/sec.
55. ftp> bin
56. 200 Type set to I.
57. ftp> get users01.dbf
58. 200 PORT Command successful
59. 150 BIN Data Connection
60. 226 BIN Transfer Complete
61. ftp: 5251072 bytes received in 7.97Seconds 
         658.69Kbytes/sec.


Lines 1 through 6 in Listing 5 show how I connect to the FTP server running on the server named prolin1 on port 7787. Line 6 shows the FTP server as being of type Oracle XML DB/Oracle Database. Lines 7 and 8 show how I enter the user and password to connect to the server. Because ASM resides on a database, this is actually the database user and password. In this case, I have used the SYSTEM database user.

Next Steps


LEARN more about ASM
oracle.com/technetwork/documentation

Once loged in, I can go to the directory containing the files to start the FTP process. But ASM files are not really file system files; they are pointers that appear as files to the database only. How can FTP see ASM files and directories?

This is where the Oracle XML DB access makes it easier. Through the Oracle XML DB FTP port, ASM disk groups are available outside the database via a virtual file system: /sys/asm. In line 11, I change the directory to the virtual file system /sys/asm.

In line 13, I issue an ls command to see which files are available. It shows the contents of the ASM storage (lines 16 through 20). Then I can change the directory to any one of them, such as USERDG2 (in line 23).

Finally, I transfer the users01.dbf file. Because this is an Oracle datafile, I FTP it by using binary mode—not the default ASCII—which I set with the bin command (line 55). Then I transfer the file to the local directory, by issuing the get command (line 57). This transfers the virtual file from ASM storage and creates an OS file with the same name (users01.dbf). When you use ASM storage for Oracle Data Pump dump files, this is a perfect way to FTP them to a remote location.

HTTP Access. Recall from the last section that I created two ports—one for FTP (7787) and one for HTTP (8080)—and showed how I used FTP on port 7787. I can download an ASM file with a Web browser as well, by using the HTTP port. Because I assigned port 8080 for HTTP, I access the Web listener running on that port. I type the following URL into my browser: 

http://prolin1:8080


The browser connects to Oracle XML DB via HTTP and displays the results shown in Figure 1. I click on the hyperlink sys and then asm ; I then see all the disk groups. I can click on the individual files to download them to the local disk.

 

figure 1
Figure 1: ASM files accessed by HTML client


Conclusion


Command-line ASM management with ASMCMD requires no SQL. It also opens up possibilities for scripting ASM operations. The FTP and HTTP interfaces—available through Oracle XML DB—provide access to ASM files and the ability to copy them and use them as conventional OS files. 


Arup Nanda (arup@proligence.com) has been an Oracle DBA for more than 12 years, handling all aspects of database administration—from performance tuning to security and disaster recovery. He is a coauthor of PL/SQL for DBAs (O'Reilly Media, 2005). He was Oracle Magazine's DBA of the Year in 2003.

 



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