kdump speed issues

Solution Verified - Updated -

Issue

  • As we had always troubles to get reasonable fast dumps I took another attempt to figure out what's going on here.

  • I did a "time dd if=/proc/vmcore of=/dev/null" to find out a maximum read performance with about 20MB/s.

  • The kdump operation time of RHEL6 is much longer than RHEL5's one, because reading /proc/vmcore is slower on RHEL6.
  • kdump(2nd kernel) in RHEL6.0 is much slower than that in RHEL5.5.
  • I/O performance in which vmcore is collected by "core_collector cp":

    RHEL5.5: About 121.9MB/s
    RHEL6.0: About 12.2MB/s
    
  • I/O performance in which vmcore is collected by "core_collector makedumpfile":

    RHEL5.5: About 118.7MB/s
    RHEL6.0: About 19.2MB/
    
  • This is performance REGRESSION from RHEL5.5.

Environment

  • Red Hat Enterprise Linux (RHEL) 6.0
  • kernel-2.6.32-71.*

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