Aren't you just looking at the same thing from two different perspective? In one case you say: I have 100% of useful data, and I need to add 50% of parity for a total of 150% raw data. In the other, you say: Out of 100% of raw data, 2/3 is useful data, 1/3 is parity, which gives you your 33.3% overhead. But it's the exact same thing, it just depends on whether you consider your overhead as a percentage of total (raw) data, or as a percentage of useful data. -- Ben ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Tuesday, July 28, 2020 10:32 PM, David Orman <ormandj@xxxxxxxxxxxx> wrote: > I'm having a hard time understanding the EC usable space vs. raw. > > https://ceph.io/geen-categorie/ceph-erasure-coding-overhead-in-a-nutshell/ > indicates "nOSD * k / (k+m) * OSD Size" is how you calculate usable space, > but that's not lining up with what i'd expect just from k data chunks + m > parity chunks. > > So, for example, k=4, m=2. you'd expect every 4 byte object written would > consume 6 bytes, so 50% overhead. however, the prior formula in a 7 server > cluster, using 4+2 encoding, would indicate 66.67% usable capacity vs. raw > storage. > > What am I missing here? > > ceph-users mailing list -- ceph-users@xxxxxxx > To unsubscribe send an email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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