On Sun, May 29, 2011 at 02:53:01PM +0200, Goswin von Brederlow wrote: > > Yes. But it's more than that. If you write to a CoW based filing system, > > fsync (and even fdatasync) will ensure the CoW metadata is also flushed > > to the device, whereas sync_file_range won't. Without the CoW metadata > > being written, the data itself is not really written. > > Which just means that a CoW based filing system or sparse files don't > support FUA. The idea of a FUA is that it is cheaper than a FLUSH. But > if nbd-server does fsync() in both cases then it is pointless to > announce FUA support.
No, that's not entirely true. With a FLUSH, you need to ensure that whatever the FLUSH would cover is flushed to disk; with a FUA, you need to ensure the same thing for just one call, which is easier to do. [...] -- The volume of a pizza of thickness a and radius z can be described by the following formula: pi zz a ------------------------------------------------------------------------------ vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1 _______________________________________________ Nbd-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/nbd-general
