[Borgbackup] Reducing backup times for raw VM images, with zfs send?

[Mason Schmitt]

> > My experience with backing up KVM sparse disk image files is that
> > even if there have been very few changes to the VMs (mostly just
> > writes to files in /var/log) backups still take several hours to a
> > locally attached USB 3 disk.
>
> I doubt it is USB3 fault, as a SSD on a Rpi4 read speed is an average of
> 235 MB/s.
>
> Did you change the --chunker-params or did you left it genuine ?
>

I didn't change the chunker-params.  Is there an optimum setting for
backing up sparse, raw, VM images?  Is the optimal setting different
between 1.1.x and 1.2.x?

I'm still running 1.1.17, which is the latest version on EPEL for CentOS
7.  However, given that 1.2 has better sparse file support and an improved
chunker, I'm wondering whether it might be worth stepping outside EPEL and
instead using pip.  Have you noticed a big performance improvement for
large sparse files, like VM images, with 1.2?

--
Mason
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