[ceph-users] Erasure Coding Pools and PG calculation - documentation

Christian Wuerdig christian.wuerdig at gmail.com
Sun Nov 12 20:57:38 PST 2017


Well, as stated in the other email I think in the EC scenario you can
set size=k+m for the pgcalc tool. If you want 10+2 then in theory you
should be able to get away with 6 nodes to survive a single node
failure if you can guarantee that every node will always receive 2 out
of the 12 chunks - looks like this might be achievable:
http://ceph.com/planet/erasure-code-on-small-clusters/

On Mon, Nov 13, 2017 at 1:32 PM, Tim Gipson <tgipson at ena.com> wrote:
> I guess my questions are more centered around k+m and PG calculations.
>
> As we were starting to build and test our EC pools with our infrastructure we were trying to figure out what our calculations needed to be starting with 3 OSD hosts with 12 x 10 TB OSDs a piece.  The nodes have the ability to expand to 24 drives a piece and we hope to eventually get to around a 1PB cluster after we add some more hosts.  Initially we hoped to be able to do a k=10 m=2 on the pool but I am not sure that is going to be feasible.  We’d like to set up the failure domain so that we would be able to lose an entire host without losing the cluster.  At this point I’m not sure that’s possible without bringing in more hosts.
>
> Thanks for the help!
>
> Tim Gipson
>
>
> On 11/12/17, 5:14 PM, "Christian Wuerdig" <christian.wuerdig at gmail.com> wrote:
>
>     I might be wrong, but from memory I think you can use
>     http://ceph.com/pgcalc/ and use k+m for the size
>
>     On Sun, Nov 12, 2017 at 5:41 AM, Ashley Merrick <ashley at amerrick.co.uk> wrote:
>     > Hello,
>     >
>     > Are you having any issues with getting the pool working or just around the
>     > PG num you should use?
>     >
>     > ,Ashley
>     >
>     > Get Outlook for Android
>     >
>     > ________________________________
>     > From: ceph-users <ceph-users-bounces at lists.ceph.com> on behalf of Tim Gipson
>     > <tgipson at ena.com>
>     > Sent: Saturday, November 11, 2017 5:38:02 AM
>     > To: ceph-users at lists.ceph.com
>     > Subject: [ceph-users] Erasure Coding Pools and PG calculation -
>     > documentation
>     >
>     > Hey all,
>     >
>     > I’m having some trouble setting up a Pool for Erasure Coding.  I haven’t
>     > found much documentation around the PG calculation for an Erasure Coding
>     > pool.  It seems from what I’ve tried so far that the math needed to set one
>     > up is different than the math you use to calculate PGs for a regular
>     > replicated pool.
>     >
>     > Does anyone have any experience setting up a pool this way and can you give
>     > me some help or direction, or point me toward some documentation that goes
>     > over the math behind this sort of pool setup?
>     >
>     > Any help would be greatly appreciated!
>     >
>     > Thanks,
>     >
>     >
>     > Tim Gipson
>     > Systems Engineer
>     >
>     >
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