Hello Axel,
On 2020-02-24 T 11:41 +0100 Axel Braun wrote:
> Am Sonntag, 23. Februar 2020, 22:36:33 CET schrieb Matthias G. Eckermann:
> > On 2020-02-23 T 17:03 +0100 Axel Braun wrote:
> > > Except that I feel that one should not use btrfs on a 32GB
> > > SD card
> >
> > one of the reasons to use btrfs for the RPi image (I know
> > that at least for SUSE Linux Enterprise) is that it is
> > compressed and thus the low IO-throughput of the SD card
> > interface is accelerated; assuming a compression rate for
> > the OS part of more than 30%, the performance factor should
> > be similar for reads and writes.
>
> Thanks for the information!
>
> So the old rule (i remember some discussions on the factory
> mailing list from some time ago) that btrfs on less than 40GB
> is not recommended, is not valid any longer?
well. I would have never called this "40GiB" a "rule", but more
a "recommendation" for a btrfs root filesystem *with* snapshots
enabled, and this recommendation has a *lot* of safety buffer
included.
Mind that this heavily depends on the
- distribution
and
- your personal way of applying updates.
To add some details:
* For a Tumbleweed with add-hoc updates enabled, I would
rate 40 GiB the lower limit, indeed, better more, as
you have a lot of change, thus lots of snapshots and
lots of metadata.
* For a Leap or SUSE Linux Enterprise with, let's say,
planned weekly updates, you can easily work with a
btrfs filesystem as small as twice the size of the OS
installation, or for an extra buffer three times:
MINIMAL_SIZE=$(( 3* $( du -msx / | cut -d'/' -f1) ))
I personally run (all my) systems with a 32 GiB root
filesystem with snapshots enabled, and the number of
snapshots limited to 8 in total.
That said, for a Raspberry Pi and an SD card, I would recommend
to apply updates rather carefully and not in tumbleweed style,
because the SD card might not like this too much:-/ Thus, a
32 GiB filesystem (with compression enabled this is equivalent
to 42 GiB or more effectively) should be very comfortable.
Hope this helps.
So long -
MgE
--
Matthias G. Eckermann, Director Product Management Linux Platforms
SUSE Software Solutions Germany GmbH - Maxfeldstr. 5 - 90409 Nürnberg
(HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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