Crystal clear, thanks for the tutorial :-) On 03/12/2013 16:52, James Pearce wrote: > It shouldn't happen, provided the sustained write rate doesn't exceed the sustained erase capabilities of the device I guess. Daily fstrim will not hurt though. > > Essentially the mapping between LBAs and physical cells isn't persistent in SSDs (unlike LBA and physical sectors on an HDD). Provided the SSD has a free cell, a write is committed to an available (pre-charged) cell and the mapping table updated. In the process, the cell that contained the now 'overwritten' (from the OS perspective) data is marked as part of the free pool, so cleared in the background ready to accept some future write. > > Under-provisioning maintain this mode of operation since LBAs that have never had a write (at least since a TRIM operation) will have no physical backing, i.e. cells will be free for the controller to use in the background. > > Some reasonable background info here: http://en.wikipedia.org/wiki/Write_amplification > > Hope that helps. > > On 2013-12-03 15:10, Loic Dachary wrote: >> On 03/12/2013 13:38, James Pearce wrote: >>> Since the journal partitions are generally small, it shouldn't need to be. >>> >>> For example implement with substantial under-provisioning, either via HPA or simple partitions. >>> >> >> Does that mean the problem will happen much later or that it will >> never happen ? As far as I understand it is just postponing it but I >> just discover this and may be completely mistaken :-) >> >> Cheers >> >>> On 2013-12-03 12:18, Loic Dachary wrote: >>>> Hi Ceph, >>>> >>>> When an SSD partition is used to store a journal >>>> >>>> https://github.com/ceph/ceph/blob/master/src/os/FileJournal.cc#L90 >>>> >>>> how is it trimmed ? >>>> >>>> http://en.wikipedia.org/wiki/Trim_%28computing%29 >>>> >>>> Cheers >>>> >>>> _______________________________________________ >>>> ceph-users mailing list >>>> ceph-users@xxxxxxxxxxxxxx >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> >>> _______________________________________________ >>> ceph-users mailing list >>> ceph-users@xxxxxxxxxxxxxx >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Loïc Dachary, Artisan Logiciel Libre
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