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03 Sep 2010

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	Interpret error counters

Solution The volume information page contains a section Error Counters where non-recoverable and recoverable volume errors over the volume lifetime are accumulated.

Non-recoverable write and read errors

These errors indicate usually a defect medium and cause PresSTORE to flag the medium as suspect. The medium can still be reused, but mostly, the volume will report non-recoverable errors again.
Keep in mind that there may be other reasons causing the supect flag to be set. E.g., in case an unexpected volume is found in the "wrong" slot of a jukebox, it may as well be flagged as suspect, even if no access errors occurred.

Recoverable write and read errors

Recoverable errors are shown as re-writes and re-reads in the user interface.
PresSTORE does not interpret these counters on it's own, the values are shown as informative items. These errors indicate that either the medium itself is old or worn out, or that the drive is dirty and needs cleaning.
There are ways to gather experience about the drive's behaviour. Unfortunately, each drive has its own characteristics, depending on the technology. Sometimes, 100's of recovered errors are quite normal, sometimes they indicate the tape is nearly worn out. Because of that, there are no general absolute numbers that can be used to rate the usability of a volume.

It is recommended to:

note the error counter(s) of a new medium and of a medium that is no longer usable. In case of using media of different brands, evaluate the counters per brand. When you have both counters, you can easily rate the estimated life time of a volume by comparing the value against the known range.
note if counters of a particular volume are significantly higher than the counters of other volumes. In such case the volume is not as good as the others. Remember that the absolute counter values must be interpreted in relation to the counters of the other media.
note if counters of all volumes increase by a similar amount. This is probably an indicator for a dirty drive.

Keywords: rewrite reread soft error counter hard error write error read error

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16 Apr 2007 09:33 AM