Re: Debian tool for creating drive images from mounted devices?

From	Stefan Monnier <monnier@iro.umontreal.ca>
Newsgroups	linux.debian.user
Subject	Re: Debian tool for creating drive images from mounted devices?
Date	2026-05-07 21:10 +0200
Message-ID	<MScgG-3lIO-11@gated-at.bofh.it> (permalink)
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> My guess is it would run 'sync' once or twice before beginning a
> snapshot, or maybe some more sophisticated equivalent. I think we'd know
> by now if it didn't.

I think we'd know if it did because `sync` can take an awfully long time
and the whole system should stall all new writes during that time: it
would be quite disruptive.

Instead when I read

    This facility does require that the snapshot be made at a time when
    the data on the logical volume is in a consistent state - the
    VFS-lock patch for LVM1 makes sure that some filesystems do this
    automatically when a snapshot is created, and many of the
    filesystems in the 2.6 kernel do this automatically when a snapshot
    is created without patching.

I understand it to mean "just as consistent as a real drive would be at the
time of a power loss".  So there's no need to empty the journal or stall
new writes: just make sure the journal entries "up to now" have reached
the underlying device: the result is not necessarily "clean", but it
is consistent.

> Any database being used for an important purpose should be using
> atomic transactions as far as possible, for example.

IIUC the LVM facility described above is indeed meant to allow
preserving the atomicity properties across the LVM layer.

=== Stefan

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Debian tool for creating drive images from mounted devices? Hans <hans.ullrich@mail.de> - 2026-05-07 10:50 +0200
  Re: Debian tool for creating drive images from mounted devices? Geert Stappers <stappers@stappers.nl> - 2026-05-07 11:00 +0200
    Re: Debian tool for creating drive images from mounted devices? Hans <hans.ullrich@mail.de> - 2026-05-07 11:40 +0200
  Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 12:40 +0200
    Re: Debian tool for creating drive images from mounted devices? Tim Woodall <debianuser@woodall.me.uk> - 2026-05-10 12:50 +0200
  Re: Debian tool for creating drive images from mounted devices? Joe <joe@jretrading.com> - 2026-05-07 12:40 +0200
    Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 12:50 +0200
      Re: Debian tool for creating drive images from mounted devices? Jochen Spieker <ml@well-adjusted.de> - 2026-05-07 15:10 +0200
        Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 15:30 +0200
          Re: Debian tool for creating drive images from mounted devices? Jochen Spieker <ml@well-adjusted.de> - 2026-05-07 16:10 +0200
        Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-07 16:00 +0200
          Re: Debian tool for creating drive images from mounted devices? Jochen Spieker <ml@well-adjusted.de> - 2026-05-07 16:10 +0200
            Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-07 18:00 +0200
              Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 19:00 +0200
                Re: Debian tool for creating drive images from mounted devices? Joe <joe@jretrading.com> - 2026-05-07 20:00 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 20:20 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-10 14:50 +0200
                Re: Debian tool for creating drive images from mounted devices? Arno Lehmann <al@its-lehmann.de> - 2026-05-11 14:30 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-11 15:00 +0200
                Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-11 17:50 +0200
                Re: Debian tool for creating drive images from mounted devices? Arno Lehmann <al@its-lehmann.de> - 2026-05-11 18:30 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-11 18:40 +0200
                Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-11 22:00 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-11 18:30 +0200
                Re: Debian tool for creating drive images from mounted devices? Andy Smith <andy@strugglers.net> - 2026-05-11 19:50 +0200
                Re: Debian tool for creating drive images from mounted devices? Arno Lehmann <al@its-lehmann.de> - 2026-05-11 22:00 +0200
                Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-12 08:00 +0200
                Re: Debian tool for creating drive images from mounted devices? Andy Smith <andy@strugglers.net> - 2026-05-12 13:40 +0200
                Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-07 21:10 +0200
  Re: Debian tool for creating drive images from mounted devices? Arno Lehmann <al@its-lehmann.de> - 2026-05-07 13:10 +0200
    Re: Debian tool for creating drive images from mounted devices? Hans <hans.ullrich@mail.de> - 2026-05-07 13:40 +0200
    Re: Debian tool for creating drive images from mounted devices? Hans <hans.ullrich@mail.de> - 2026-05-07 13:40 +0200
      Re: Debian tool for creating drive images from mounted devices? Charles Curley <charlescurley@charlescurley.com> - 2026-05-07 15:50 +0200
        Re: Debian tool for creating drive images from mounted devices? <tomas@tuxteam.de> - 2026-05-07 16:20 +0200
        Re: Debian tool for creating drive images from mounted devices? "Roy J. Tellason, Sr." <roy@rtellason.com> - 2026-05-07 20:30 +0200
      Re: Debian tool for creating drive images from mounted devices? Andy Smith <andy@strugglers.net> - 2026-05-07 18:30 +0200

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