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 >>>> [email protected] >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> >>> _______________________________________________ >>> ceph-users mailing list >>> [email protected] >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
-- Loïc Dachary, Artisan Logiciel Libre
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