User's Manual

114 Managing media

actual layout of the remigrated data on FSE media differs from the original data layout on the unreadable

medium.

Figure 23 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. Note that this variable affects all types of maintenance jobs.

NOTE: 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 a redundant copy of an FSE medium only when the medium is

already damaged and has the status set to unusable. You can also perform this action with a worn-out

medium that has the status set to unreliable and even with a medium that can be read and written to.

This way you avoid losing a migrated data copy before the problem arises or becomes more severe.

After creating a redundant copy of an unreliable or a “good” (usable) medium, two valid (readable) data

copies exist in the same FSE media pool. Note that you cannot have more than two valid copies of the

same data in the same media pool.

CAUTION: If you use the command fsemedium --copy-contents with a “good” (usable) medium

that has empty or open volumes with free space, the redundant copy recreation process may start creating

the redundant copy on the same medium. In this case, the newly created additional copy does not

increase data safety.

Media Pool 2

Media Pool 4

F4 F5' F6 F3 F4

F2 F6F3 F4''F4'

F5'F5''

F5''