[GTALUG] Compressing an image of a microSD card

[Giles Orr]

On Thu, 14 May 2020 at 18:04, Lennart Sorensen via talk
<talk at gtalug.org> wrote:>
> On Thu, May 14, 2020 at 05:20:18PM -0400, D. Hugh Redelmeier via talk wrote:
> > If your filesystem lives on some form of flash (SSD, SD card, USB
> > stick, ...) this can reduce the lifetime and performance of your
> > hardware.
> >
> > The wear-levelling firmware of the drive will think that every block of
> > the drive is "live" (contains valuable information).  This will increase
> > "write amplification".
> >
> > In any case, if you do do this, be sure to use fstrim afterwards.  (I'm
> > not sure that SD cards and USB sticks support trim.
>
> I think the idea was to do it on the image loop back mounted, not on
> the original device.

What all this discussion has made me realize is that I have to either
A) modify the original SD card or B) loop mount and modify the backup.
Option A was what I was initially proposing, but forcing a write
(zeroing out most of the contents) across the whole card isn't a great
idea.  Not terrible, but not great.  Option B involves modifying the
backup, and I think this is a worse idea because 1) a backup should be
an accurate recreation of the source, and 2) modifying the backup
effectively means you'd be restoring something different, and do I
really feel comfortable counting on that?

The more I think about it, the less I want to modify either of them.
Thanks for clarifying the process: it solidified my opinion on what
should be done (although not in the direction I expected).  ie. 10G
really ain't that big, I'll just keep the backup as is.  Thanks
everyone.

-- 
Giles
https://www.gilesorr.com/
gilesorr at gmail.com