An archive will miss data if there were read errors during a restore, and in case error correcting codes were used, if there were too many read errors to correct them all.
When restoring archives with missing data, two things can happen depending on how large the `holes' in the archive are:
There are three sources of information about missing data:
Also, the restore index file usually contains archiver error messages that were produced when processing the `holes' in the archive. The files listed immediately before or after an error message may be damaged or missing completely. For example, with the restore log
usr/src/utils/Makefile -- uncompressed
usr/src/utils/proto.h -- okay
gzip: stdin: invalid compressed data--crc error
afio: "inentry xwait()": Exit 1
usr/src/utils/utils.c -- uncompressed
usr/src/utils/utils.h -- uncompressed
the files proto.h
and utils.c
may have been restored incorrectly.
Also, the original archive may have contained a one or more files
between proto.h
and utils.c
that are now lost completely.
Unfortunately, the archiver can sometimes restore a file incorrectly
because of a hole without giving any error message. However, if a
file is listed as -- uncompressed
and is not immediately preceded by
an error message, you can safely assume it was restored correctly.
Another way of checking if files were restored right is by looking at
their contents. If a file was listed as -- okay
in a restore of
an archive with a hole in it, and the hole was in the file, the
archiver will in general not produce an error message in the restore
log: it will say -- okay
but it is wrong. The hole in the
restored file will however always be `filled' by trestore with
?????
characters. A quick way of checking all files in a
directory for this is by running the command
grep -l "????????????" *
in this directory. This will list all the names of files with
sequences of ?????
characters in them.
If a floppy is missing completely from a backup set, and you use the
q!
command of trestore to go on to the next floppy, in rare cases
the holes in restored files will be filled with the string This is
dummy data
in stead of ?????
.
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