On 16/09/15 06:54, Chris Friesen wrote: > On 09/15/2015 01:16 AM, Clay Gerrard wrote: >> Idk about a chestnut, but there's this: >> >> http://lists.openstack.org/pipermail/openstack-operators/2011-October/000297.html >> > > That advice isn't quite accurate. It says "Enabling barriers > effectively turns all writes into Write-Through operations, so the write > goes straight to the disk platter and you get little performance benefit > from the raid card (which hurts a lot in terms of lost iops)." > > That's actually not necessarily true. It's complicated (See > http://marc.info/?l=linux-scsi&m=136674609728515&w=2 for discussion) but > from what I understand most hardware RAID controller vendors will not > actually flush their non-volatile cache on a SCSI "SYNCHRONIZE CACHE" > command. They will ensure that the data is in the NV cache, and then > return to the host. (Which should be quick.) > > This gets you the best of both worlds...you get the reliability of > filesystem barriers enforcing ordering through the OS stack, with the > performance benefit of not having to flush the data all the way down to > the disks. >
Funny - the Ceph guys are discussing this very issue (in particular with Intel SSD, but the thread is generally informative...and quite long): https://www.mail-archive.com/ceph-users@lists.ceph.com/msg23037.html _______________________________________________ Mailing list: http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack Post to : openstack@lists.openstack.org Unsubscribe : http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
