Hi, Am 29.01.2015 07:53, schrieb Christian Balzer: > On Thu, 29 Jan 2015 01:30:41 +0000 Ramakrishna Nishtala (rnishtal) wrote: >> * Per my understanding once writes are complete to journal then >> it is read again from the journal before writing to data disk. Does this >> mean, we have to do, not just sync/async writes but also reads >> ( random/seq ? ) in order to correctly size them? >> > You might want to read this thread: > https://www.mail-archive.com/ceph-devel@xxxxxxxxxxxxxxx/msg12952.html > > Assuming this didn't change (and just looking at my journal SSDs and OSD > HDDs with atop I don't think so) your writes go to the HDDs pretty much in > parallel. > > In either case, an SSD that can _write_ fast enough to satisfy your needs > will definitely have no problems reading fast enough. > due, that the data are in the cache (ram), there are only marginal reads from the journal-ssd! iostat from an journal ssd: Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sdc 304,45 0,16 82750,46 29544 15518960008 I would say, if you have much more reads, you have to less memory. Udo _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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