If k=8,m=3 is too slow on HDDs, so you need replica 3 and SSD DB/WAL, vs EC 8,3 on SSD, then that's (1/3) / (8/11) = 0.45 multiplier on the SSD space required vs HDDs. That brings it from 6x to 2.7x. Then you have the benefit of not needing separate SSDs for DB/WAL both in hardware cost and complexity. SSDs will still be more expensive; but perhaps justifiable given the performance, rebuild times, etc. If you only need cold-storage, then EC 8,3 on HDDs will be cheap. But is that fast enough? On Tue, Dec 3, 2019 at 3:47 PM <jesper@xxxxxxxx> wrote: > > >> * Hardware raid with Battery Backed write-cache - will allow OSD to ack > >> writes before hitting spinning rust. > > > > Disagree. See my litany from a few months ago. Use a plain, IT-mode HBA. > > Take the $$ you save and put it toward building your cluster out of SSDs > > instead of HDDs. That way you don’t have to mess with the management > > hassles of maintaining and allocating external WAL+DB partitions too. > > These things are not really comparable - are they? Cost of SSD vs. HDD is > still in the 6:1 favor of HHD's. Yes SSD would be great but not > nessesarily affordable - or have I missed something that makes the math > work ? > > -- > Jesper > _______________________________________________ > 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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