Re: [ceph-users] what's the difference between pg and pgp?
PG = Placement Group PGP = Placement Group for Placement purpose pg_num = number of placement groups mapped to an OSD When pg_num is increased for any pool, every PG of this pool splits into half, but they all remain mapped to their parent OSD. Until this time, Ceph does not start rebalancing. Now, when you increase the pgp_num value for the same pool, PGs start to migrate from the parent to some other OSD, and cluster rebalancing starts. This is how PGP plays an important role. Karan Singh Systems Specialist , Storage Platforms CSC - IT Center for Science, Keilaranta 14, P. O. Box 405, FIN-02101 Espoo, Finland mobile: +358 503 812758 tel. +358 9 4572001 fax +358 9 4572302 http://www.csc.fi/ > On 22 May 2015, at 02:06, Florent MONTHEL wrote: > > To be sure to understand, if I create 2 times replicated pool toto with 1024 > pgs and 1 pgp, pg and data of pool toto will be mapped on only 2 OSDs and on > 2 servers right ? > > Sent from my iPhone > >> On 21 mai 2015, at 18:58, Florent MONTHEL wrote: >> >> Thanks Ilya for this clear explanation! >> I'm searching that for a long time >> >> Best practices is to have pg = pgp in order to "avoid" using of the same set >> of osd right ? (On a small cluster you will have) >> >> Sent from my iPhone >> On 21 mai 2015, at 07:49, Ilya Dryomov wrote: On Thu, May 21, 2015 at 12:12 PM, baijia...@126.com wrote: Re: what's the difference between pg and pgp? >>> >>> pg-num is the number of PGs, pgp-num is the number of PGs that will be >>> considered for placement, i.e. it's the pgp-num value that is used by >>> CRUSH, not pg-num. For example, consider pg-num = 1024 and pgp-num >>> = 1. In that case you will see 1024 PGs but all of those PGs will map >>> to the same set of OSDs. >>> >>> When you increase pg-num you are splitting PGs, when you increase >>> pgp-num you are moving them, i.e. changing sets of OSDs they map to. >>> >>> Thanks, >>> >>> Ilya >>> ___ >>> ceph-users mailing list >>> ceph-users@lists.ceph.com >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > ___ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com smime.p7s Description: S/MIME cryptographic signature ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] what's the difference between pg and pgp?
To be sure to understand, if I create 2 times replicated pool toto with 1024 pgs and 1 pgp, pg and data of pool toto will be mapped on only 2 OSDs and on 2 servers right ? Sent from my iPhone > On 21 mai 2015, at 18:58, Florent MONTHEL wrote: > > Thanks Ilya for this clear explanation! > I'm searching that for a long time > > Best practices is to have pg = pgp in order to "avoid" using of the same set > of osd right ? (On a small cluster you will have) > > Sent from my iPhone > >>> On 21 mai 2015, at 07:49, Ilya Dryomov wrote: >>> >>> On Thu, May 21, 2015 at 12:12 PM, baijia...@126.com >>> wrote: >>> Re: what's the difference between pg and pgp? >> >> pg-num is the number of PGs, pgp-num is the number of PGs that will be >> considered for placement, i.e. it's the pgp-num value that is used by >> CRUSH, not pg-num. For example, consider pg-num = 1024 and pgp-num >> = 1. In that case you will see 1024 PGs but all of those PGs will map >> to the same set of OSDs. >> >> When you increase pg-num you are splitting PGs, when you increase >> pgp-num you are moving them, i.e. changing sets of OSDs they map to. >> >> Thanks, >> >> Ilya >> ___ >> ceph-users mailing list >> ceph-users@lists.ceph.com >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] what's the difference between pg and pgp?
Thanks Ilya for this clear explanation! I'm searching that for a long time Best practices is to have pg = pgp in order to "avoid" using of the same set of osd right ? (On a small cluster you will have) Sent from my iPhone > On 21 mai 2015, at 07:49, Ilya Dryomov wrote: > >> On Thu, May 21, 2015 at 12:12 PM, baijia...@126.com >> wrote: >> Re: what's the difference between pg and pgp? > > pg-num is the number of PGs, pgp-num is the number of PGs that will be > considered for placement, i.e. it's the pgp-num value that is used by > CRUSH, not pg-num. For example, consider pg-num = 1024 and pgp-num > = 1. In that case you will see 1024 PGs but all of those PGs will map > to the same set of OSDs. > > When you increase pg-num you are splitting PGs, when you increase > pgp-num you are moving them, i.e. changing sets of OSDs they map to. > > Thanks, > >Ilya > ___ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] what's the difference between pg and pgp?
Le 21/05/2015 13:49, Ilya Dryomov a écrit : > On Thu, May 21, 2015 at 12:12 PM, baijia...@126.com wrote: >> Re: what's the difference between pg and pgp? > > pg-num is the number of PGs, pgp-num is the number of PGs that will be > considered for placement, i.e. it's the pgp-num value that is used by > CRUSH, not pg-num. For example, consider pg-num = 1024 and pgp-num > = 1. In that case you will see 1024 PGs but all of those PGs will map > to the same set of OSDs. > > When you increase pg-num you are splitting PGs, when you increase > pgp-num you are moving them, i.e. changing sets of OSDs they map to. > > Thanks, > > Ilya > ___ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > Seems like i said a huge stupid thing ;-) I'm gonna learn about a new feature of ceph... I apologize ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] what's the difference between pg and pgp?
On Thu, May 21, 2015 at 12:12 PM, baijia...@126.com wrote: > Re: what's the difference between pg and pgp? pg-num is the number of PGs, pgp-num is the number of PGs that will be considered for placement, i.e. it's the pgp-num value that is used by CRUSH, not pg-num. For example, consider pg-num = 1024 and pgp-num = 1. In that case you will see 1024 PGs but all of those PGs will map to the same set of OSDs. When you increase pg-num you are splitting PGs, when you increase pgp-num you are moving them, i.e. changing sets of OSDs they map to. Thanks, Ilya ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] what's the difference between pg and pgp?
Le 21/05/2015 11:12, baijia...@126.com a écrit : > > > > baijia...@126.com Hi, weird question.. There's no relationship at all...Oh, yes a single letter ;-) pg stands for placement group in ceph storage pgp stands for Pretty Good Privacy, a crypto based software. But Wikipedia is your best friend. Btw, you could use subject for ...the subject of your email; to sum-up the main idea, and you the body of your email to detail, to be more specific on your quesiton. Best regards ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
[ceph-users] what's the difference between pg and pgp?
baijia...@126.com___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
