Re: Small RGW objects and RADOS 64KB minimun size

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Will there be a well documented strategy / method for changing block sizes
on existing clusters? Is there anything that could be done to optimize or
assist clusters in the cut over?

On Tue, Feb 16, 2021 at 3:41 AM Loïc Dachary <loic@xxxxxxxxxxx> wrote:

> Hi Josh :-)
>
> Thanks for the update: this is great news and I look forward to using this
> once Pacific is released.
>
> Cheers
>
> On 16/02/2021 00:43, Josh Durgin wrote:
> > Hello Loic!
> >
> > We have developed a strategy in pacific - reducing the min_alloc_size
> for HDD to 4KB by default.
> >
> > Igor Fedotov did a lot of investigation and benchmarking, and came up
> > with some improvements to bluestore [1][2] to make this change have
> > little performance impact (it even increases performance in many cases).
> >
> > Josh
> >
> > [0] https://github.com/ceph/ceph/pull/34588
> > [1] https://github.com/ceph/ceph/pull/33434
> > [2] https://github.com/ceph/ceph/pull/33365
> >
> > On 2/14/21 9:21 AM, Loïc Dachary wrote:
> >> Bonjour,
> >>
> >> Reading Karan's blog post about benchmarking the insertion of billions
> objects to Ceph via S3 / RGW[0] from last year, it reads:
> >>
> >>> we decided to lower bluestore_min_alloc_size_hdd to 18KB and re-test.
> As represented in chart-5, the object creation rate found to be notably
> reduced after lowering the bluestore_min_alloc_size_hdd parameter from 64KB
> (default) to 18KB. As such, for objects larger than the
> bluestore_min_alloc_size_hdd , the default values seems to be optimal,
> smaller objects further require more investigation if you intended to
> reduce bluestore_min_alloc_size_hdd parameter.
> >>
> >> There also is a mail thread dated 2018 on this topic as well, with the
> same conclusion although using RADOS directly and not RGW[3]. I read the
> RGW data layout page in the documentation[1] and concluded that by default
> every object inserted with S3 / RGW will indeed use at least 64kb. A pull
> request from last year[2] seems to confirm it and also suggests modifying
> bluestore_min_alloc_size_hdd  has adverse side effects.
> >>
> >> That being said, I'm curious to know if people developed strategies to
> cope with this overhead. Someone mentioned packing objects together client
> side to make them larger. But maybe there are simpler ways to do the same?
> >>
> >> Cheers
> >>
> >> [0]
> https://www.redhat.com/en/blog/scaling-ceph-billion-objects-and-beyond
> >> [1] https://docs.ceph.com/en/latest/radosgw/layout/
> >> [2] https://github.com/ceph/ceph/pull/32809
> >> [3] https://www.spinics.net/lists/ceph-users/msg45755.html
> >
>
> --
> Loïc Dachary, Artisan Logiciel Libre
>
>
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