On Fri, Sep 21, 2012 at 11:51 AM, Andre Robatino
> Renich Bon Ciric <renich <at> woralelandia.com> writes:
>> Didn't know about this. Should this be published somewhere on the
>> front/download page? This is great. Thanks!
> The following issues should be noted:
> 1) In F15, the xz compression used changed, and unfortunately that isn't handled
> automatically, so to use delta ISOs between versions after that, you need to
> rebuild the ISOs on a machine running F15 or later. I do have semi-static
> binaries in http://robatino.fedorapeople.org/deltaiso_executables/ that can be
> used to rebuild recent ISOs on older OSes (F14 or below, or RHEL/CentOS, for
> example), but as long as you're running F15 or later, just install the deltaiso
> package from the Fedora repo and use the applydeltaiso command from that.
> 2) Since this involves delta rpms, there's the same bandwidth/CPU speed tradeoff
> that's involved in deciding whether or not to use yum-presto for updates. If you
> have a very fast download and a not-so-fast CPU, downloading full updated
> packages becomes faster than downloading and applying delta rpms. In this case,
> you could use rsync instead, which is available on at least some of the mirrors.
> The yum-presto code for F18 and above will be threaded and make use of multiple
> cores for rebuilding, which will make yum-presto more favorable, but the
> deltaiso code isn't threaded yet (although it should be possible).
> 3) If you have the old ISO burned to optical disc, and you want to read it off
> and verify the checksum before downloading the delta ISO (which is a good idea),
> you need to know the exact size to read off. This is tricky. You can't just do
> something like "cat /dev/sr0 > file.iso" and expect to get the right size. You
> need to find the exact size, and then either use a dd command to read off
> exactly that much, or use the truncate command on a padded image to reduce it to
> the right size. To get the right size, you can look up the image at
> http://dl.fedoraproject.org/pub/archive/ , then start a download with wget,
> which shows the exact size in bytes at the beginning, then Ctrl-C it. With
> standard ISOs, you would be able to look in the ISO header to find the size, but
> all recent Fedora ISOs are "hybrid" which means they have extra padding in
> addition to the ISO header size. Currently the extra padding consists of zeros
> up to the next largest multiple of 1 MiB, so it's possible to infer the size,
> but that may change in the future. I avoid all this myself by writing the exact
> size of the image on my discs itself right after burning them (i.e.,
> "3,834,642,432 bytes" on the Fedora-17-x86_64-DVD.iso disc).
Wow! Noted, thanks!
It's hard to be free... but I love to struggle. Love isn't asked for;
it's just given. Respect isn't asked for; it's earned!
Renich Bon Ciric
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