Chunqiang Tang wrote: > > Based on my limited understanding, I think FVD shares a > > lot in common with the COW format (block/cow.c). > > > > But I think most of the advantages you mention could be considered as > > additions to either qcow2 or qed. At any rate, the right way to have > > that discussion is in the form of patches on the ML. > > FVD is much more advanced than block/cow.c. I would be happy to discuss > possible leverage, but setting aside the details of QCOW2, QED, and FVD, > let’s start with a discussion of what is needed for the next generation > image format.
Thank you for the detailed description. FVD looks quite good to me; it seems very simple yet performant at the same time, due to its smart yet simple design. > Moreover, using a host file system not only adds overhead, but > also introduces data integrity issues. Specifically, if I/Os uses O_DSYNC, > it may be too slow. If I/Os use O_DIRECT, it cannot guarantee data > integrity in the event of a host crash. See > http://lwn.net/Articles/348739/ . You have the same issue with O_DIRECT when using a raw disk device too. That is, O_DIRECT on a raw device does not guarantee integrity in the event of a host crash either, for mostly the same reasons. -- Jamie
