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Groups > linux.debian.user > #286581
| From | Arno Lehmann <al@its-lehmann.de> |
|---|---|
| Newsgroups | linux.debian.user |
| Subject | Re: Debian tool for creating drive images from mounted devices? |
| Date | 2026-05-11 14:30 +0200 |
| Message-ID | <MTxVM-4luO-7@gated-at.bofh.it> (permalink) |
| References | <MSbuh-3l9v-11@gated-at.bofh.it> <MTbLz-46bP-3@gated-at.bofh.it> <MTbLz-46bP-1@gated-at.bofh.it> |
| Organization | IT-Service Arno Lehmann |
Hi all,
Am 10.05.2026 um 14:41 schrieb tomas@tuxteam.de:
> On Sun, May 10, 2026 at 01:54:10PM +0200, Thomas Schmitt wrote:
>> Hi,
>>
>> Jochen Spieker wrote:
>>>> I was always under the impression that an LVM snapshot is not better
>>>> than an unclean filesystem, like for example after a power loss. But
>>>> this 20 year old document proved me wrong:
>>>> https://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html
>>
>> tomas@tuxteam.de:
>>> Is there any reference for that? AFAIK LVM doesn't "know" about the
>>> underlying file system (if there is any).
>> In a later mail:
>>> This sounds very hypothetical: how should LVM that there is a file
>>> system /at all/ on the logical volume being snapshotted? How that
>>> this file system is mounted?
>>
>> Obviously one can inquire the list of mounted filesystems and their
>> storage devices [...]
>
> ...then fsfreeze
>
> Woah, Thomas: you definitely rock :)
>
> Just what we all needed.
Do we? On one of my debian systems, man fsfreeze gets me
DESCRIPTION
fsfreeze suspends or resumes access to a filesystem.
fsfreeze halts any new access to the filesystem and creates a
stable image on disk. fsfreeze is intended to be used with
hardware RAID devices that support the creation of snapshots.
fsfreeze is unnecessary for device-mapper devices. The device-
mapper (and LVM) automatically freezes a filesystem on the device
when a snapshot creation is requested. For more details see the
dmsetup(8) man page.
Although LVM is rather limited in its support for snapshots, and XFS
being somewhat paranoid (which is good for file systems) make this
challenging in many cases.
Because, to get back to the original topic -- an LVM snapshot is *not*
an exact copy of the original volume, and of course much less so of the
partition, disk, or anything else. So a block level dump of an LVM
snapshot is not something you can just dump back as a disaster recovery
step.
And. of course, it doesn't let gaps between block storage consistency,
file system consistency, file system "cleanness", file contents
consistency and application data consistency vanish.
Cheers,
Arno
> Thank you (and for all your other insightful
> posts here!)
> Cheers
--
Arno Lehmann
IT-Service Lehmann
Sandstr. 6, 49080 Osnabrück
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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
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Re: Debian tool for creating drive images from mounted devices? Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-07 16:00 +0200
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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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