From: "Piotr Dałek" <branch@predictor.org.pl>
To: Zhen Cao <juehuiconst@gmail.com>
Cc: ceph-devel@vger.kernel.org
Subject: Re: Ceph PG Number
Date: Wed, 30 Nov 2016 09:31:05 +0100 [thread overview]
Message-ID: <20161130083105.GM26997@predictor> (raw)
In-Reply-To: <CAOmt5rK42=8DcdrkeHgqsY6o2NjaQ+5wWOeZToZNsPd0GtS2ew@mail.gmail.com>
On Wed, Nov 30, 2016 at 04:22:10PM +0800, Zhen Cao wrote:
> Hi,
> I am reading the RADOS paper,but i could not understand why more PGs
> per OSD result in a more balanced distribution.I konw the mapping
> procedure between oid and osd，but it is neverless difficult to
> understand for me.
> Thanks for your help!
In a nuthshell - because each PG corresponds to multiple objects.
And because of this, it is possible that some PGs will aggregate more
objects than other PGs, resulting in lack of acutal balance. Also see here:
http://docs.ceph.com/docs/jewel/rados/operations/placement-groups/
--
Piotr Dałek
branch@predictor.org.pl
http://blog.predictor.org.pl
next prev parent reply other threads:[~2016-11-30 8:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-30 8:22 Ceph PG Number Zhen Cao
2016-11-30 8:31 ` Piotr Dałek [this message]
2016-11-30 14:18 ` Sage Weil
[not found] ` <CAOmt5rKynSwpdtXGDFJXD956mbLf5rR6XAg7p8wDwfpJk=RgUw@mail.gmail.com>
2016-12-01 2:44 ` Fwd: " Zhen Cao
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