system hangs during dump + compress > usb2-drive

Jin Guojun jguojun at
Sun Sep 30 05:49:58 UTC 2012

In FreeBSD 8.3 release (possibly in earlier release),  dump a file system has 
2-3GB or more
 content can cause system hang in a  specific  case (pipe to compression):

dump FS-on-SATA-drive >  usb-drive         OK
dump FS-on-SATA-drive | anyCompress >  sata-drive         OK
mv a-large-dump-file from STAT drive to a USB drive         OK
dump small-FS-on-SATA-drive | anyCompress >  usb-drive         OK
small -- 1.8GB or less
dump large-FS-on-SATA-drive | anyCompress >  usb-drive         hang
content is 3GB or larger (did not try around 2GB yet)

When system hangs, no sub system, such video, network, etc, will function.
Typically, the unfinished compressed dump file is around 1.5-2.7GB, so
guessing dumped file content is close to
or over 2GB when failure occurred.

Has anyone encountered the same problem?
Because this usually takes a few hours to occur, this is hard to watch
how/when it happens.
Is any way to debug or determine what status the system is?


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