Re: [PLUG] disk image one-liner

[Rich Freeman <r-plug@thefreemanclan.net>]

On Wed, Apr 27, 2016 at 12:13 AM, JP Vossen <jp@jpsdomain.org> wrote:
> Ahhh, so XFS only.  Very cool though, thanks.
>

I don't think xfsdump is atomic.  Some filesystems support atomic
dumps, and some don't.  Any filesystem that journals has the potential
to support it.  (To do an atomic dump the filesystem would start
jounaling all data once the dump starts and not delete the journal
entries until the dump is complete, so that the original state of the
filesystem isn't lost until the dump is over.)

btrfs send only works on a snapshot, so it is always atomic.  I
imagine that the zfs equivalent works similarly, and both should work
online.

If you're looking for an fs-agnostic archiver there is fsarchive,
which I suspect uses tools like xfsdump/etc underneath.  It will also
resize filesystems on the fly during restore.

There is also partimage which is the main engine behind clonezilla.
It uses a somewhat unique approach in that the only filesystem-aware
logic it has is determining which blocks are used/free. It then does a
block-level save of all the used blocks.  That means it won't do
things like resizing, and the destination device has to be at least as
large as the source since it won't consolidate the used space when the
image is restored.  For the more exotic filesystems that it supports
which are otherwise not welll-supported on linux it is probably the
safest option short of dd since it tries to faithfully make the copy
identical to the source, minus blocks it thinks weren't used.  Of
course, dd would be the safest option since it makes no assumptions at
all.

In general though, most unix-y filesystems tend to have some kind of
dump program which is intended to be used for backups.  For ext2/3/4
the program is typically just called "dump" and it actually uses those
two numbers at the end of your fstab that nobody understands.

-- 
Rich
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