restore/read errors: summary

From: John Rust (
Date: Tue Jan 26 1993 - 20:36:14 CST

Dear Sirs:

        About a week ago I posted a query about problems reading a
        tape written using the dump command. This note summarizes
        the responses I received.

1. the problem
         restore generates a "tape media error" halfway
        into a tape written by the following dump dump command:

        /usr/etc/dump 1cusdtf 610 1200 18 /dev/rst0 /dev/sd2a

        Doing "restore ivf" and selecting a certain
        file or directory on this tape I get:

        read error while skipping over inode 182405
        st0: Error for command 'read', Error Level: 'Fatal'
        Block: 59976 File Number: 0
                Sense Key: Media Error

2. suggested solutions

   A. Perhaps the most helpful general suggestion I received
        is **don't use dump on an active filesystem!**. It appears
        that my tape isn't bad, but the problem was caused by
        changes in the file system after dump was started. It
        happens that I had installed my system swap file on /dev/sd2a
        and this is exactly where the read error occurs. So the
        first remedy was to move the swap file to a different
        filesystem and I find that I no longer get these kind of
        read errors using restore. The man pages really ought to offer
        a clearer warning of this problem with dump. All that it
        says is:
BUGS It is recommended that incremental dumps also be performed
             with the system running in single-user mode.

   B. Given that I cannot ever gaurantee my /dev/sd2a is
        quiescent and given that I want automated backups to
        occur via crontab, I have decided not to use dump anymore.
        I now use GNU tar (available via anonymous ftp from which is a form of tar that allows
        multi-volume and incremental backups on an active filesystem.
   C. However this is preventive medicine. How do I recover the
        valuable files on my tape? I haven't been able to yet!
        Perhaps the most helpful suggestion I received is
        to try the following:

        dd if=/dev/sd2a conv=noerror | restore ivf -

        But alas this doesn't work either. I am afraid I have had
        to give up on this one and send the tape to a commercial
        firm that specializes in tape recovery. There are several
        such companies listed in the back of Byte and InforWorld.
        These firms are expensive and do not guarantee recovery.
        If and when they succeed I will post a followup message
        indicating how much it cost and how the company succeeded
        in recovering the file (if they are willing to tell me how
        they did it).
        Professor John Rust
        Department of Economics (608) 262-0488 (office)
        University of Wisconsin (608) 238-8708 (home)
        Madison, WI 53706 (608) 262-4747 (fax)

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