Hi Willem, the SSDs are probably fine for backing OSDs, it's the O_DSYNC writes they tend to lie about.
They may have a failure rate higher than enterprise-grade SSDs, but are otherwise suitable for use as OSDs if journals are placed elsewhere. On Mon, Jan 9, 2017 at 2:39 PM, Willem Jan Withagen <[email protected]> wrote: > On 9-1-2017 18:46, Oliver Humpage wrote: > > > >> Why would you still be using journals when running fully OSDs on > >> SSDs? > > > > In our case, we use cheaper large SSDs for the data (Samsung 850 Pro > > 2TB), whose performance is excellent in the cluster, but as has been > > pointed out in this thread can lose data if power is suddenly > > removed. > > > > We therefore put journals onto SM863 SSDs (1 journal SSD per 3 OSD > > SSDs), which are enterprise quality and have power outage protection. > > This seems to balance speed, capacity, reliability and budget fairly > > well. > > This would make me feel very uncomfortable..... > > So you have a reliable journal, so upto there thing do work: > Once in the journal you data is safe. > > But then you async transfer the data to disk. And that is an SSD that > lies to you? It will tell you that the data is written. But if you pull > the power, then it turns out that the data is not really stored. > > And then the only way to get the data consistent again, is to (deep)scrub. > > Not a very appealing lookout?? > > --WjW > > > _______________________________________________ > ceph-users mailing list > [email protected] > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- Brian Andrus Cloud Systems Engineer DreamHost, LLC
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