mdflush(8) System Manager's Manual mdflush(8)
NAME
mdflush - Trace md flush events. Uses Linux eBPF/bcc.
SYNOPSIS
mdflush
DESCRIPTION
This tool traces flush events by md, the Linux multiple device driver
(software RAID). The timestamp and md device for the flush are printed.
Knowing when these flushes happen can be useful for correlation with
unexplained spikes in disk latency.
This works by tracing the kernel md_flush_request() function using dy-
namic tracing, and will need updating to match any changes to this
function.
Note that the flushes themselves are likely to originate from higher in
the I/O stack, such as from the file systems.
Since this uses BPF, only the root user can use this tool.
REQUIREMENTS
CONFIG_BPF and bcc.
EXAMPLES
Trace md flush events:
# mdflush
FIELDS
TIME Time of the flush event (HH:MM:SS).
PID The process ID that was on-CPU when the event was issued. This
may identify the cause of the flush (eg, the "sync" command),
but will often identify a kernel worker thread that was managing
I/O.
COMM The command name for the PID.
DEVICE The md device name.
OVERHEAD
Expected to be negligible.
SOURCE
This is from bcc.
https://github.com/iovisor/bcc
Also look in the bcc distribution for a companion _examples.txt file
containing example usage, output, and commentary for this tool.
OS
Linux
STABILITY
Unstable - in development.
AUTHOR
Brendan Gregg
SEE ALSO
biosnoop(8)
USER COMMANDS 2016-02-13 mdflush(8)
Generated by dwww version 1.16 on Tue Dec 16 05:46:54 CET 2025.