To ensure the most efficient use of media, you may want to eliminate wasted space on the media by compacting and reformatting the media. The following topics provide details:
◆ “When media reuse is necessary” on page 116
◆ “Understanding the media reuse process” on page 116
When media reuse is necessary
DiskXtender writes files sequentially to most removable media types. When you edit a file on the extended drive that has been written sequentially to rewritable media, DiskXtender does not edit the file data on the media. Instead, when a migrated file is edited, the file is written as a new file to the next blank area on the media, and the file tag on the extended drive is updated to point to the new file. The old file data still remains on the media, but is orphaned. This is true for DVD-RAM, MO, UDO, and tape media.
Similarly, when you delete a file that has been written sequentially to these media types, the file and its data are deleted only from the extended drive and are not removed from the media. Deleting the file on the extended drive removes the file tag, which contains the location information for the file on the media. Without the file tag, DiskXtender can no longer track that file on the media (even though the data is still there), and the file is orphaned.
The only exception to this is when a file is renamed on rewritable media. In that case, the file trailer on the rewritable media, where the filename is kept, is updated to reflect the new filename.
The space taken up by older versions of files and deleted files is wasted space on the media. “Understanding the media reuse process” on page 116 provides details on how to reuse the media and minimize the amount of wasted space.
Understanding the media reuse process
You can reclaim this wasted space on media and use the media more efficiently by:
1. Returning all valid versions of files to the extended drive through compaction.
2. Rewriting the files to another piece of media.
3. Reformatting the media.
4. Writing new files to the media.
When you compact a piece of media, DiskXtender evaluates each file on the media. If there is a file tag on the extended drive for a file on the piece of media, the file data is copied back to the extended drive and the migration information for the file is removed. In this way, the file appears as if it has never been migrated to media.
IMPORTANT
If you allow folder renames on media that does not support folder renames, then do not compact the media. Data loss might occur because DiskXtender will not find the corresponding file tags on the extended drive, so the files will not be copied back to the drive.
DiskXtender then evaluates the file against configured move rules. Because the files have already been written to media once, they usually qualify for migration as soon as they are copied back to the extended drive. This means that the files are migrated back to media as soon as the file migration schedule is active (and a background scan occurs, if an age delay is configured for the assigned move rules).
When DiskXtender finishes evaluating each file on a piece of media during
compaction, the media is automatically removed from the media group to which it is assigned. The media can then be reformatted, labeled, and assigned to a media group.
This enables DiskXtender to begin migrating new files to the media.
Note: You can compact other removable media types, including DVD-R, MO WORM, UDO WORM, and tape-WORM. However, you cannot reformat those media types. After the files are copied back to the extended drive through compaction and the media is removed from its media group, it remains assigned to the extended drive. The files also remain on the media.
You can deallocate the media and remove it from the system. If you add the media to a media group again instead, the files are restored—again—to the extended drive, and DiskXtender continues writing files to the media from the point at which it last stopped. As a result, you cannot reuse these media types.
You can configure DiskXtender to automatically reuse media based on the amount of wasted space on the media. You can also monitor the media by using DiskXtender reports, and then manually perform the steps to reuse the media at the appropriate time.
Automatically reusing media
If you use DVD-RAM, MO, UDO, or tape media in a device configured as part of a MediaStor media service, then you can configure DiskXtender to automatically compact a piece of media, reformat it, re-label it, and re-add it to a media group. This automatic reuse occurs based on the percentage of wasted space on the media, and is configured by using media group automation features.
After the automatic compaction, media is reformatted with the same file system that was originally on the media. It is then labeled based on the configured label
specifications, and added to the same media group.
To configure automatic reuse of DVD-RAM, MO, UDO, or tape media:
1. Ensure that there is sufficient free space on the extended drive to accommodate the files that are written back to the extended drive during compaction. At a minimum, the equivalent of one side of the media should be available. If you use media compression, then keep in mind that you may need as much as four times the amount of space on one side of the media.
Purge inactive data to free space on the extended drive, as discussed in Chapter 12, “Purging Files.”
2. When configuring a media group with removable media, select Auto-label blank media when free space falls below ___ MB in the Media Labeling section on the Automation page, as illustrated in Figure 20 on page 118.
Figure 8 Media group Automation page
3. Choose whether to use a standard labeling method or barcodes:
• To use a standard method:
a. Select Use standard method.
b. In the Label Prefix text box, type a prefix for the media label.
c. From the Number Width drop-down list, select the number of digits to be used to create the incremental numbering for the media label.
The Sample Name text box provides an example of the label based on the prefix and number width criteria you set. For example, if you type Payroll as the prefix and select a number width of 3, the label for the first piece of media is Payroll001, the second is Payroll002, and so forth.
• To use barcodes, select Use barcode.
4. If there are multiple libraries configured and you want to limit the selection of blank media for the media group to a single library, select the Restrict blank media search to this library checkbox, and then select the library from the drop-down list.
5. In the Media Compaction section, select Auto-compact media when wasted space exceeds ___ %, and the type the percentage of wasted space that must be on the media before DiskXtender automatically compacts the media.
Note: If media compaction fails, some, all, or none of the files from the media might have been moved back to the extended drive. If you can determine the cause of the compaction failure, make the appropriate adjustments and reschedule the compaction. The compaction process starts over, but any files already copied back to the extended drive are not duplicated. In addition, all files that have been compacted are re-migrated to media as they qualify for movement.
Monitoring and manually reusing media
If you use DVD-RAM, MO, UDO, or tape media, then you can monitor the status of an individual piece of media. When the amount of wasted space on the media reaches a certain point, you can assign media tasks to compact the media, reformat it, and re-label it. You can then re-add it to a media group and begin migrating files to it.
To monitor and manually reuse a piece of media:
1. Monitor the properties for the media on a regular basis to determine the amount of wasted space on the media:
a. Right-click the piece of media and select Properties.
The Media Properties dialog box appears.
b. Click the Location tab.
c. Make a note of the Byte Count value in the Extended Drive section. This is the amount of space in bytes on the extended drive that is occupied by files that have been written to the media.
d. Click the Space tab.
e. Make a note of the Used Space value in the Logical Capacity section. This is the amount of data in bytes that has been written to the media.
f. Divide the byte count on the extended drive by the used space on the media to determine the percentage of wasted space on the media.
g. If the percentage is high, proceed with the rest of this procedure to reuse the media. The default percentage of wasted space at which DiskXtender initiates media reuse as part of the media group automation process is 50 percent.
2. Right-click the piece of media and select Edit Tasks.
3. Select COMPACT from the Next Task drop-down list, and then click Add Next Task.
The Compact task appears in the task list of the Media Tasks dialog box, as illustrated in Figure 21 on page 120.
Figure 9 Compact media task
4. Choose whether to process the media task as soon as possible or when the next media task schedule is active.
By default, the media task schedule is active at the same time as the file migration schedule (daily from 8 P.M. to 8 A.M).
5. Select FORMAT from the Next Task drop-down list, and then click Add Next Task.
The Format task appears below the Compact task in the task list of the Media Tasks dialog box, as illustrated in Figure 22 on page 120.
Figure 10 Format media task after Compact media task
6. From the File System drop-down list, select the file system with which to format the media.
7. Leave the Force low-level SCSI format checkbox clear to perform a quick format on the media. A low-level SCSI format is not necessary.
8. If the library and file system support it, choose whether to enable compression for the media by selecting or clearing the checkbox.
9. To reformat a piece of tape media as tape-WORM, select the Convert this media to WORM checkbox. This option is available only if you are formatting the media in a Quantum DLT-S4 drive.
Note: Once tape has been formatted and converted to tape-WORM, it cannot be converted back to tape. However, a tape can be reformatted and converted to tape-WORM.
10. In the When To Process section of the Media Tasks dialog box, select the same scheduling option that you selected for the Compact media task.
11. Select LABEL from the Next Task drop-down list, and then click Add Next Task.
The Label task appears below the Format task in the task list of the Media Tasks dialog box, as illustrated in Figure 23 on page 121.
Figure 11 Label media task after Compact and Format media tasks 12. Type a label for the media in the Media Name text box.
13. In the When To Process section of the Media Tasks dialog box, select the same scheduling option that you selected for the Compact and Format media tasks.
14. Click Next.
The Order Media in Task Queue page appears with the recently added media at the bottom of the media task queue list.
15. (Optional) Promote or demote the media in the list to change the order in which tasks are processed by clicking the up or down arrow to the right of the list box.
16. Click Finish.
All media with tasks assigned appear in the Media Task Queue Manager until they are processed. Media with tasks selected to process as soon as possible may appear only briefly in the queue before the processing completes.
17. Add the media to a media group.
Troubleshooting a Compact media task
When you run a Compact media task, you might encounter the following issues:
◆ Extended drive space issues
If, during the processing of the Compact task, the extended drive becomes so full as to not be able to receive any more files, the Compact task goes into a suspended state for one hour. In addition, no other Compact tasks for other media are processed until the original hour (for which the attempted Compact task was suspended) has expired. After an hour has passed, DiskXtender retries the original compaction, and if the task is successful, processes any remaining Compact tasks.
This suspension of all Compact tasks enables DiskXtender to move and purge files to clear necessary extended drive space, and it ensures that drives, which might be needed to complete other media functions, are not being used to attempt Compact tasks that cannot succeed until there is sufficient space on the extended drive.
◆ Compact task failure
If a Compact media task fails, some, all, or none of the files from the media might have been moved back to the extended drive. If you can determine the cause of the compaction failure, make the appropriate adjustments and reschedule the compaction. The compaction process starts over, but any files already copied back to the extended drive are not duplicated. In addition, all files that have been compacted are re-migrated to media as they qualify for movement.