You should be protected against single component failures, yes, that's the point of journals.
It's important to ensure that on-disk volatile cache -- these days in the 8-128MB range -- remain turned off, otherwise it usually presents an opportunity for data loss especially when power drops. Disk manufactures tout cache size but are quiet about the fact that it's always turned off by default for just this reason. Some LSI firmware and storcli versions have a bug that silently turns this on. RAID HBA's also introduce an opportunity for data loss, with their on-card caches. HBA cache not protected by a BBU / supercap has a similar vulnerability, and in some cases are just plain flaky and rife with hassles. I'm not immediately finding a definitive statement about the number of journal writes required for ack. > So, which is correct, all replicas must be written or only min_size before > ack? > > But for me the takeaway is that writes are protected - even if the journal > drive crashes, I am covered. > > - epk > > -----Original Message----- > From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of > Anthony D'Atri > Sent: Friday, May 20, 2016 1:32 PM > To: ceph-users@lists.ceph.com > Subject: Re: [ceph-users] Do you see a data loss if a SSD hosting several OSD > journals crashes > > >> Ceph will not acknowledge a client write before all journals (replica >> size, 3 by default) have received the data, so loosing one journal SSD >> will NEVER result in an actual data loss. > > Some say that all replicas must be written; others say that only min_size, 2 > by default, must be written before ack. > > --aad > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > Legal Disclaimer: > The information contained in this message may be privileged and confidential. > It is intended to be read only by the individual or entity to whom it is > addressed or by their designee. If the reader of this message is not the > intended recipient, you are on notice that any distribution of this message, > in any form, is strictly prohibited. If you have received this message in > error, please immediately notify the sender and delete or destroy any copy of > this message! _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
