Hello, what has been said by others before is essentially true, as in if you want: - as much data conservation as possible and have - RAID controllers with decent amounts of cache and a BBU then disabling the on disk cache is the way to go. But as you found out, w/o those caches and a controller cache to replace them, performance will tank. And of course any data only in the pagecache (dirty) and not yet flushed to the controller/disks is lost anyway in a power failure. All current FS _should_ be powerfail safe (barriers) in the sense that you may loose the data in the disk caches (if properly exposed to the OS and the controller or disk not lying about having written data to disk) but the FS will be consistent and not "all will be lost". I'm hoping that this is true for Bluestore, but somebody needs to do that testing. So if you can live with the loss of the in-transit data in the disk caches in addition to the pagecache and/or you trust your DC never to loose power, go ahead and get re-enable the disk caches. If you have the money and need for a sound happy sleep, do the BBU controller cache dance. Some controllers (Areca comes to mind) actually manage to IT mode style exposure of the disks and still use their HW cache. Christian -- Christian Balzer Network/Systems Engineer chibi@xxxxxxx Rakuten Communications _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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