[ironic] [tripleo] RFC: lzma vs gzip for compressing IPA initramfs

Arne Wiebalck arne.wiebalck at cern.ch
Mon Nov 30 09:22:56 UTC 2020

On 30.11.20 10:10, Mark Goddard wrote:
> On Fri, 27 Nov 2020 at 17:37, Arne Wiebalck <arne.wiebalck at cern.ch> wrote:
>> Hi,
>> I did a quick test (one data point):
>> - the image build time increased by 10 mins
>>     (on a VM, this is more than double compared to gzip)
>> - but: the resulting image size is ~30% smaller (421 vs 297 MB)
>> - the cleaning time (unpacking on bare metal!) increased by ~30 seconds
> 30 seconds is a long time, even for bare metal. 134 MB is roughly to a
> gigabit of network traffic. So really this comes down to how much
> spare capacity you have in your network to handle bursts of these
> downloads.

 From what I understand the main issue Dmitry is trying to address
with this proposal is to reduce the risk of (UEFI) boot issues due
to memory constraints on the target host.

>> So, lzma looks like a good option to reduce the image size which
>> we had to do in our deployment already to address boot issues
>> (we removed some packages).
>> Keeping gzip as the default and offering lzma as an option to
>> start with as suggested by Sergii seems like a good way forward.
>> I also think it would be good to have someone else test as well
>> to have another data point :-)
>> Cheers,
>>    Arne
>> On 27.11.20 14:00, Sergii Golovatiuk wrote:
>>> Hi,
>>> LZMA causes very high CPU and memory usage for creating images, leaving
>>> less resources for other processes. If Ironic is running alongside with
>>> other services that may cause significant impact for them. I would leave
>>> gzip option as default, would introduce --lzma as well as --gzip and use
>>> lzma on 5-10% of our CI resources to test how it goes. Then after a
>>> significant amount of testing we could turn it on as default. Proper
>>> deprecation should be applied here as well IMHO.
>>> чт, 26 нояб. 2020 г. в 17:57, Dmitry Tantsur <dtantsur at redhat.com
>>> <mailto:dtantsur at redhat.com>>:
>>>      Hi folks,
>>>      I've been playing with ways to reduce the size of our IPA images.
>>>      While package removals can only save us tens of megabytes, switching
>>>      from gzip to lzma reduces the size by around a third (from 373M to
>>>      217M in my testing).
>>>      What's the caveat? The unpacking time increases VERY substantially.
>>>      On my nested virt lab the 217M image took around 5 minutes to
>>>      unpack. I'm not sure how much it will impact real bare metal, please
>>>      feel free to test
>>>      https://review.opendev.org/c/openstack/ironic-python-agent-builder/+/764371
>>>      and tell me.
>>>      So, what do you think? Switching to lzma by default will likely
>>>      affect CI run time (assuming we still have DIB jobs somewhere...)
>>>      and development environments, but it will also provide a visible
>>>      reduction in the image size (which benefit all environments). Large
>>>      TripleO images may particularly benefit from this (but also
>>>      particularly affected by the unpacking time).
>>>      Feedback is very welcome.
>>>      Dmitry
>>>      --
>>>      Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
>>>      Commercial register: Amtsgericht Muenchen, HRB 153243,
>>>      Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs,
>>>      Michael O'Neill
>>> --
>>> SergiiGolovatiuk
>>> Senior Software Developer
>>> Red Hat <https://www.redhat.com/>
>>> <https://www.redhat.com/>

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