Re: [ceph-users] bluestore_allocated vs bluestore_stored
Earlier in bluestore's life, we couldn't handle a 4K min_alloc size on NVMe without incurring pretty significant slowdowns (and also generally higher amounts of metadata in the DB). Lately I've been seeing some indications that we've improved the stack to the point where 4K min_alloc no longer is significantly slower on NVMe than 16K. It might be time to consider switching back for Octopus. On the HDD side I'm not sure if we want to consider dropping down from 64K. There are definitely going to be some trade-offs there. Mark On 6/17/19 3:22 AM, Igor Fedotov wrote: Hi Maged, min_alloc_size determines allocation granularity hence if object size isn't aligned with its value allocation overhead still takes place. E.g. with min_alloc_size = 16K and object size = 24K total allocation (i.e. bluestore_allocated) would be 32K. And yes, this overhead is permanent. Thanks, Igor On 6/17/2019 1:06 AM, Maged Mokhtar wrote: Hi all, I want to understand more the difference between bluestore_allocated and bluestore_stored in the case of no compression. If i am writing fixed objects with sizes greater than min alloc size, would bluestore_allocated still be higher than bluestore_stored ? If so, is this a permanent overhead/penalty or is something the allocator can re-use/optimize later as more objects are stored ? Appreciate any help. Cheers /Maged ___ 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 ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] bluestore_allocated vs bluestore_stored
Hi Maged, min_alloc_size determines allocation granularity hence if object size isn't aligned with its value allocation overhead still takes place. E.g. with min_alloc_size = 16K and object size = 24K total allocation (i.e. bluestore_allocated) would be 32K. And yes, this overhead is permanent. Thanks, Igor On 6/17/2019 1:06 AM, Maged Mokhtar wrote: Hi all, I want to understand more the difference between bluestore_allocated and bluestore_stored in the case of no compression. If i am writing fixed objects with sizes greater than min alloc size, would bluestore_allocated still be higher than bluestore_stored ? If so, is this a permanent overhead/penalty or is something the allocator can re-use/optimize later as more objects are stored ? Appreciate any help. Cheers /Maged ___ 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
[ceph-users] bluestore_allocated vs bluestore_stored
Hi all, I want to understand more the difference between bluestore_allocated and bluestore_stored in the case of no compression. If i am writing fixed objects with sizes greater than min alloc size, would bluestore_allocated still be higher than bluestore_stored ? If so, is this a permanent overhead/penalty or is something the allocator can re-use/optimize later as more objects are stored ? Appreciate any help. Cheers /Maged ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
