Messages in this thread | | | Date | Mon, 26 Nov 2001 17:11:50 -0800 | From | Andrew Morton <> | Subject | Re: Journaling pointless with today's hard disks? |
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"H. Peter Anvin" wrote: > > Followup to: <9tumf0$dvr$1@cesium.transmeta.com> > By author: "H. Peter Anvin" <hpa@zytor.com> > In newsgroup: linux.dev.kernel > > > > Indeed; having explicit write barriers would be a very useful feature, > > but the drives MUST default to strict ordering unless reordering (with > > write barriers) have been enabled explicitly by the OS. > > > > On the subject of write barriers... such a setup probably should have > a serial number field for each write barrier command, and a "WAIT FOR > WRITE BARRIER NUMBER #" command -- which will wait until all writes > preceeding the specified write barrier has been committed to stable > storage. It might also be worthwhile to have the equivalent > nonblocking operation -- QUERY LAST WRITE BARRIER COMMITTED. >
For ext3 at least, all that is needed is a barrier which says "don't reorder writes across here". Asynchronous behaviour beyond that is OK - the disk is free to queue multiple transactions internally as long as the barriers are observed. If the power goes out we'll just recover up to and including the last-written commit block.
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