Re: ODROID XU4 and UEFI - Re: Cautionary tale: how to kill an SDCard with one simple command
On Wed, Jul 25, 2018 at 08:15:03PM +0000, Mark Morgan Lloyd wrote:
> Really depends what you mean by an "image backup". I do a lot of stuff using
> "ye olde traditional" dd, either between devices or more often making an
> image of the entire device (i.e. including partition table etc.) to a file
> and manipulate it there (e.g. by deleting a directory tree /after/ the data
> has been copied).
>
> However when using something like dd there's a major problem: you either
> want the storage medium to be removed so you can copy the filesystems
> offline, or you need to shut every possible piece of running software down
> (including things like your SSH daemon) so that nothing's writing to the
> disc when you're trying to copy it. Needless to say the same considerations
> apply when using dd to do a sector-by-sector copy from one device to
> another.
man fsfreeze
Some filesystems (at least btrfs) can also enumerate all writes since a
certain point of time, which allows backing up the full filesystem even
without freezing writes, with incremental versions done very cheaply.
> There are still ways of working round that sort of problem. For example, you
> can copy an entire device using dd to capture boot segments and partition
> layout, inspect and recreate the filesystems using mkfs, then use
> [something] to copy files one at a time into the new filesystems taking care
> that some bootloaders need a wakeup call when a file moves.
Usually dd-ing the partition table and u-bootage, then rsync on filesystem
data works pretty well. Unlike btrfs ways, rsync is not atomic, but most
people consider it good enough.
Meow!
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