User's Manual

hp StorageWorks File System Extender User Guide 101
which multiple copying was configured. This process is called recreating a redundant copy and is
available for FSE tape media and FSE disk media.
By recreating the redundant copy of the damaged migrated data, you can restore the availability and
safety of the migrated data.
The redundant copy recreation process
Redundant copy recreation is started by the fsemedium command and performed by an FSE
maintenance job. The process first scans the File System Catalog (FSC) to find the file generations that were
migrated to the specified medium, searches for alternative redundant copies in other FSE media pools, and
then remigrates data to the FSE media pool of the unreadable medium. Note that the actual layout of the
remigrated data on FSE media differs from the original data layout on the unreadable medium.
Recreating a copy of damaged migrated data
Figure 16 Recreating a copy of damaged migrated data
If alternative migrated copies of the unrecallable data exist in both tape and disk media pools, the
redundant copy is recreated from the data stored in the disk media pool. By using the disk media pool, as
many FSE drives as possible remain available for other FSE processes, such as migration and recall. You
can define the total number of drives that can be simultaneously used for redundant copy recreation (for
example, when several media are damaged) with the FSE partition configuration variable
SystemMaxNumDrivesMaint. (This variable affects all types of maintenance jobs.)
The redundant copy recreation process operates on a “best-effort” basis. It processes all file generations
that can be copied from an alternative location on FSE media and skips the files for which the copying
cannot be done. The process recreates only the generations that were migrated to the unusable medium.
In cases where no alternative migrated copies of the unreadable data exist, a warning (the unreadable
data belongs to a non-latest file generation) or an error (the unreadable data belongs to the latest file
generation) is reported to the FSE error log for each file that cannot be recreated.
NOTE: You are not restricted to creating redundant copies only in the case where FSE media is already
damaged (“unusable” media status). You can also perform this action with worn-out media (“unreliable”
media status). In this way, you can prevent the loss of a migrated data copy before the problem becomes
severe. Of course, you can create redundant media copies also while the medium is still readable.
Determining the unusable media
FSE detects read errors when recalling the migrated data from FSE disk or tape media to an HSM file
system. After a read error is detected, the status of the FSE medium is automatically set to “unusable”.
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