From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Taysom Date: Mon, 08 May 2006 12:00:43 -0600 Subject: [Ocfs2-devel] OCFS2 features RFC - separate journal? In-Reply-To: <445AC References: <20060425183553.GB10524@ca-server1.us.oracle.com> <445936FE.90401@google.com> <44594AE2.9080802@oracle.com> <44594EC9.3040407@google.com> <445A6A61.2090009@oracle.com> <445A7EF3.2000701@google.com> <20060504223037.GB21588@ca-server1.us.oracle.com> <445AC Message-ID: <445F32A9.C8CD.0002.0@novell.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com Network Appliance has been very successful with exactly this architecture. Paul >>> Daniel Phillips 05/08/06 11:43 am >>> Paul Taysom wrote: > If I was worried about NFS performance, I'd rather use NVRAM as an > immediate reply disk drive. What makes you think that that is any faster than just having a fast journal on the filesystem? It is certainly messier and adds two more data copies. Plus it only helps NFS, what if there are other servers on the node? And how do you maintain cache consistency with the data written to the NFS reply journal when it has been acknowledged but is not actually in the filesystem? On a snapshot, the NFS reply journal would be one more thing that needs to be flushed, this is one more thing needing administration attention. How much latency do you think is saved by a dedicated reply journal vs a fast filesystem journal? I doubt it is as much as you suppose, it is on the order of microseconds per write and the reply journal will eventually have to pay double for that anyway. Also, somebody has to implement your NFS reply journal, further messing up knfsd. I am having a hard time seeing what is good about a dedicated NFS reply journal. Regards, Daniel