I get '[W010] block sequence error' in my backups. What causes this?

When backing up, BRU keeps track of the blocks that it writes to for both disk and tape.  When this warning message occurs, BRU skipped a sequential block. number on the file that it indicates in the message.  Here is the official error description:

[W010] filename: warning - block sequence error
BRU detected an inconsistency in the ordering of blocks returned by the archive device on a read.
For example, BRU asked for blocks “11, 12, 13, 14, 15” and got blocks “11, 12, 14, 15, 16.” This error may indicate a hardware problem. If this message occurs at the start of the 2nd volume (when reading a multiple volume archive), it probably means that the last few blocks of the previous volume were missing or were unreadable. This can occur if the media size parameter was set too large in the brutab file (i.e. size=150M for a 60 megabyte tape) during the backup and BRU attempted to write past the end of the previous volume. With some tape drives, it may also occur if the media size was set to zero (unknown). The problem can usually be avoided by setting the media size to a value that is certain to be less than the maximum capacity of the volume (i.e. set size=149MT for a 150 megabyte tape).
To detect and avoid this problem, always verify your archive immediately after the backup is performed. AUTOSCAN does this automatically for all devices that have an entry in the brutab file (unless noautoscan is set or you are using a norewind device).

What This Means

If you are a BRU Server 1.2.0 user and you're seeing this message, it means that there was some type of error that prevented BRU Server from writing the blocks in sequential order.  There is a patch that is mandatory if you're running BRU Server on Mac OS X.  That patch is available from:


However, if you've applied this patch and you're still seeing numerous amounts of these errors, then there are a few other things that you can try to resolve the problem:
  1. Clean the tape drive.  The write head and read head are two different components.  If the write head is dirty and the read head is not, then you could end up with these types of errors.
  2. Set all Ethernet cards to a fixed speed on any system that BRU Server is installed.  This can reduce the number of TCP/IP errors that may come into play and has resolved the problem for many customers.
  3. Is this happening of every tape?  If so, make sure the drive is operating correctly.  You may also contact the drive/library manufacturer for additionally utilities to test the device.
  4. Is this happening on just a tape or two?  If so, then you may want to check the tapes themselves as this may be a sign of the tape beginning to wear out.
  5. We've seen in many cases that the tape drive firmware can actually be the culprit in some cases.  Make sure that the firmware running on your tape drive is the most up-to-date version available for your tape device.
If the above steps have not resolved the error, please contact TOLIS Group Technical Support for additional assistance.