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IBM Tivoli Storage Manager for Space Management for UNIX: User's Guide


Recalling Your Migrated Files

To return a migrated file to your workstation, access the file in the same way as you would access a file that resides on your local file system. The HSM recall daemon automatically recalls the migrated file from Tivoli Storage Manager storage. This process is referred to as transparent recall. If you want to return specific migrated files to your local file system, use selective recall. When you selectively recall a file, the HSM client stores it to its originating file system.

Whenever you recall a file to your local file system, the access time (atime) for the file changes to the current time unless you set the timestamp control mode on the dsmmode command to preserve the last recorded access time for your file. This is valid for AIX JFS file systems only.

This chapter discusses both transparent recall and selective recall.


Recalling Your Migrated Files Automatically

Attention: A transparent recall process waits for a tape drive to become available. If you migrate and back up your data to tape, use separate tape drives for both migrated data and backed up data. Otherwise, you cannot back up migrated files. To improve performance, migrate your data to disk storage instead of to tape. Performance requirements for migrated data might be more strict than for backed up data.

Transparent recall automatically returns a migrated file to its originating local file system when you access it. When you recall a file, the HSM client leaves a copy of your recalled file in storage. The file becomes premigrated because an identical copy exists both on your local file system and in storage. If you do not modify the file, it remains premigrated until it once again becomes eligible for migration.

If you modify a recalled file, it becomes a resident file. The next time your file system is reconciled, the space monitor daemon marks the stored copy for expiration.

Recall Your Files in an AIX JFS Environment

Valid for AIX JFS file systems only

In an AIX JFS environment, the HSM client provides the following two additional recall modes that recall a migrated file to its originating file system:

These recall modes are for read access on migrated files only. You cannot set a recall mode for a resident or a premigrated file.

Attention: Do not use the migrate-on-close or read-without-recall mode for a file that you migrate from a file system that an NFS server exports. Because NFS opens and closes a file many times when an NFS client accesses it, performance can be severely hindered.

To set or change recall modes on your migrated files, use the dsmattr command. The recall mode that you set for a migrated file remains associated with that file only as long as the file remains migrated. See "Use the dsmattr Command" for more information about this command.

If you change the recall mode for a migrated file, or for a specific execution of a recall process, you change how the HSM recall daemon recalls a migrated file. See "Use the dsmmode Command" for more information about this command.

If you recreate a deleted stub file, the recall mode for the file becomes normal (the default) despite what you previously set.

You can access a file using more than one process at a time. Another process can cause a file that you are accessing in migrate-on-close or read-without-recall mode to remain on your local file system as a resident or premigrated file. For example, if you set the recall mode to normal (the default) for a migrated file, and you access it with a process using the migrate-on-close recall mode and you do not modify the file, you would expect the file to be in a migrated state when you close it. But if someone else accesses the file at the same time with a process using normal recall mode or with a process that modifies the file in some way, the file remains on your local file system as either a resident or a premigrated file, depending on the actions that the other process takes.

Use the Migrate-on-Close Mode

Valid for AIX JFS file systems only

The migrate-on-close mode temporarily recalls a migrated file to its originating file system. The recalled file remains on your local file system for as long as it remains open. If you do not modify the file before you close it, the HSM client replaces it with a stub file on your local file system. It then becomes a migrated file. The copy that currently resides in Tivoli Storage Manager storage remains valid because you did not modify the file. If more than one process accesses the file at one time, the HSM client returns the file to a migrated state only if all the processes do not modify the file. If any one process modifies the file, it remains on your local file system as a resident file.

Use the dsmattr command to set the recall mode to migrate-on-close for migrated files that you normally read but that you do not modify. When you set the recall mode to migrate-on-close, this mode remains associated with your files until you:

For more information about changing recall modes on migrated files, see "Use the dsmattr Command".

Use the Read-Without-Recall Mode

Valid for AIX JFS 4.3 file systems only

The read-without-recall mode reads a migrated file from Tivoli Storage Manager storage without storing it on your local file system. The HSM client reads information sequentially from the migrated file, and caches that information in a memory buffer on your workstation. This occurs either when the processes that access the file do not modify it, or when the file is executable but the process does not execute the file. If the file is a binary executable file, the file is recalled to your local file system if a process executes it. The file remains on your local file system as a premigrated file or it is returned to a migrated state, depending on which recall mode the process used that stored it on your local file system.

Attention: Do not set the read-without-recall mode on a file that an NFS server exports. This attribute holds recalled file data in memory. It is not compatible with NFS access, which uses asynchronous reads. If you accidentally set this attribute on a file that a remote NFS client accesses, the HSM client recalls the file and automatically sets the recall attribute of the file to normal.

When you use the read-without-recall mode, the following actions can occur:

Use the read-without-recall mode for single access, sequential reads of non-executable files. Accessing a read-without-recall file with more than one process at the same time, or seeking backward in a file can significantly affect the performance of each process that accesses your files. Each of these actions can cause the HSM client to break the connection with the Tivoli Storage Manager server and start the read-without-recall process again. Each read process in progress for the file is delayed until the next piece of information it needs is cached in a memory buffer. Only a small portion of a read-without-recall file is cached in a memory buffer to keep to a minimum the memory overhead of read-without-recall files.

Using the read-without-recall mode to access more than one file can cause a conflict for resources on the Tivoli Storage Manager server. For example, if a single process opens more than one file, and those files reside on the same sequential media, the process obtains access to only one file at a time. If a process reads only the first megabyte of data from each file, and it leaves the files open for additional reads later, one or more of the reads can time out if the process has been waiting too long, and the Tivoli Storage Manager server must free resources to perform the next read.

When you set the recall mode for a migrated file to read-without-recall, that mode remains associated with your file until you:

If a file is a binary executable file and you run it with execute permission, the recall mode is normal.

|Recall Your Files in an AIX GPFS Environment

|Use the Partial File Recall Mode

| | |

|Valid for AIX GPFS HSM only

|In an AIX GPFS environment, the HSM client provides the partial file recall |mode that recalls a portion of a migrated file. This recall mode is for |read access on migrated files that were transferred without compression |only. Files that were migrated using compression will always be |recalled completely. If a file qualifies for partial file recall (if it |is larger than MINPartialrecallsize) and compression is also turned |on, the partial file recall mode prevails, and the file is sent without |compression.

|Partial file recall recalls a portion of a migrated file. This |avoids having to recall an entire, potentially large file, when only a small |portion of the file is required by an application. When HSM intercepts |a read request for such a file and the file is migrated, it will calculate |which portion of the file to recall based on the offsets contained in the read |request. This results in time and disk space savings, since only a |portion of the file is recalled, using less local disk space.

|Use the dsmattr command to set the recall mode to partial file |recall for migrated files that you normally read but that you do not |modify. When you set the recall mode to partial file recall, this mode |remains associated with your files until you: |

|You can use the following methods to specify which files HSM should recall |using partial file recall: |

|For more information about changing recall modes on migrated files, see "Use the dsmattr Command".

|Streaming Recall Mode

| | |

|Valid for AIX GPFS HSM

|Streaming recall mode allows for an asynchroneous recall of migrated |files. The recalled portion of the file can be accessed while the file |is recalled. Streaming recall mode is valid for read-only operations on |the file.

|Note: Partial file recall mode takes precedence over |streaming recall mode. If a file is smaller than its file system's |MINPartialrecallsize (as configured via the dsmmigfs - add or |update commands), or MINPartialrecallsize is set to 0, normal or |streaming recall mode takes precedence.

|You can use the following methods to specify which files HSM should recall |using streaming recall mode: |

How HSM Determines Which Recall Mode to Use

Table 13 displays the recall mode that is used depending on the:


Table 13. Recall Modes

If the recall mode for a migrated file is: And the recall mode for a process is (AIX JFS only): If the process: This recall mode is used:
Normal Normal Does not modify the file Normal. File becomes premigrated.
Normal Normal Modifies the file Normal. File becomes resident.
Normal Migrate-on-close Does not modify the file Migrate-on-close. File returned to migrated state.
Normal Migrate-on-close Modifies the file Normal. File becomes resident.
Migrate-on-close Normal Does not modify the file Migrate-on-close. File returned to migrated state.
Migrate-on-close Normal Modifies the file Normal. File becomes resident.
Migrate-on-close Migrate-on-close Does not modify the file Migrate-on-close. File returned to migrated state.
Migrate-on-close Migrate-on-close Modifies the file Normal. File becomes resident.
Read-without-recall Normal Does not:
  • Modify the file
  • Use memory mapping
  • Execute the file and the file is a binary executable file
Read-without-recall. File remains migrated.
Read-without-recall Normal
  • Modifies the file
  • Uses memory mapping
  • Executes the file and the file is a binary executable file

Normal. If modified, file becomes resident. If not modified, file becomes premigrated.
Read-without-recall Migrate-on-close Does not:
  • Modify the file
  • Use memory mapping
  • Execute the file and the file is a binary executable file
Read-without-recall. File remains migrated.
Read-without-recall Migrate-on-close
  • Uses memory mapping
  • Executes the file and the file is a binary executable file

Migrate-on-close. File returns to migrated state.
Read-without-recall Migrate-on-close Modifies the file Normal. File becomes resident.
Partial file recall Normal Does not modify the file Partial file recall. File remains migrated. If the entire file is recalled, the file becomes premigated.
Partial file recall Normal Modifies the file Normal. File becomes resident.
Streaming Normal Does not modify the file Streaming recall mode. The user application can access the file after its data (in megabytes specified with the MINStreamfilesize option of the dsmmigfs command) have been recalled.
Streaming Normal Modifies the file Normal. File becomes resident.

Recalling Your Migrated Files Selectively

Use selective recall if you want to return specific migrated files to your local file system. The access time (atime) changes to the current time when you selectively recall a migrated file.

When you selectively recall a group of files, they are recalled in the most efficient, time-saving order based on where they are stored. For example, if some of your files are stored on a disk storage device and some of your files are stored on a tape storage device, the HSM client recalls all of your files that are stored on the disk storage device first. It next recalls all of your files that are stored on the tape storage device.

For AIX JFS file systems only: Selective recall overrides the recall mode (migrate-on-close or read-without-recall) that you set for a migrated file. You can selectively recall a file regardless of the mode that you set for your file.

Use Selective Recall

To recall selected files, follow these steps:

  1. Click Selective Recall in the Hierarchical Storage Management window.
  2. Click Select File Systems in the Selective Recall window to select a file system.
  3. Select the file systems that contain the files you want to recall.
  4. Click the Select button. A directory of the file systems that you selected displays in the Directory Tree View field in the Selective Recall window.
  5. To select all files in a directory, click the Select All Files in A Directory button and select one or more directories.
  6. To select all files in all subdirectories, click the Select All Files in All Subdirectories button and select one or more subdirectories.
  7. To select individual files, click List Selection to view a list of your selected files. Select the files that you want to recall in the File List View portion of the window. The HSM client displays migrated files in the File List View window only.
  8. To display premigrated and resident files, click View->View options.
  9. Click Recall. The Selective Recall Status window displays.
  10. Click the Stop button at the bottom of the window to stop recalling files. Any recalled files remain on your local file system in a premigrated state.
  11. Click OK to close the Information Dialog box after you receive confirmation that all files are recalled.
  12. Click Return. The Selective Recall window displays.
  13. Click Cancel to close the Selective Recall window.

Using the dsmrecall Command

To selectively recall files from storage from the command line, use the dsmrecall command. For example, to recall a file named proj1rpt to the /home/proja directory, enter:

   dsmrecall /home/proja/proj1rpt
For AIX JFS file systems only: When you selectively recall a file, you override the migrate-on-close or read-without-recall mode that you previously set for a migrated file.

See dsmrecall for more information about this command.

Use the dsmattr Command

Valid for AIX JFS and AIX GPFS only

To set or change the recall mode for one or more migrated files, use the dsmattr command. Select normal, migrate-on-close, read-without-recall, partialrecall, or streaming recall mode. See dsmattr for more information about this command.

Use the dsmmode Command

Valid for AIX JFS file systems only

Use the dsmmode command to set a recall mode for a process to normal or migrate-on-close. If you set the recall mode for a file to migrate-on-close, and any process modifies the file, it remains on your local file system. When you set the recall mode to normal, the file also remains on your local file system if it is accessed by processes that use the migrate-on-close mode, and at the same time, at least one process accesses the file or modifies it using normal recall mode. See "Use the dsmmode Command" for more information about this command.


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