* We are trying to assess if we are going to see a data loss if an SSD that
is hosting journals for few OSDs crashes. In our configuration, each SSD is
partitioned into 5 chunks and each chunk is mapped as a journal drive for one
OSD. What I understand from the Ceph documentation: "Consistency: Ceph OSD
Daemons require a filesystem interface that guarantees atomic compound
operations. Ceph OSD Daemons write a description of the operation to the
journal and apply the operation to the filesystem. This enables atomic updates
to an object (for example, placement group metadata). Every few seconds-between
filestore max sync interval and filestore min sync interval-the Ceph OSD Daemon
stops writes and synchronizes the journal with the filesystem, allowing Ceph
OSD Daemons to trim operations from the journal and reuse the space. On
failure, Ceph OSD Daemons replay the journal starting after the last
synchronization operation." So, my question is what happens if an SSD fails -
am I going to lose all the data that has not been written/synchronized to OSD?
In my case, am I going to lose data for all the 5 OSDs which can be bad? This
is of concern to us. What are the options to prevent any data loss at all? Is
it better to have the journals on the same hard drive, i.e., to have one
journal per OSD and host it on the same hard drive? Of course, performance
will not be as good as having an SSD for OSD journal. In this case, I am
thinking I will not lose data as there are secondary OSDs where data is
replicated (we are using triple replication). Any thoughts? What other
solutions people have adopted for data reliability and consistency to address
the case I am mentioning?
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