Jonathan Loran wrote: > David Magda wrote: > >> On Feb 24, 2008, at 01:49, Jonathan Loran wrote: >> >> >>> In some circles, CDP is big business. It would be a great ZFS offering. >>> >> ZFS doesn't have it built-in, but AVS made be an option in some cases: >> >> http://opensolaris.org/os/project/avs/ >> > > Point in time copy (as AVS offers) is not the same thing as CDP. When > you snapshot data as in point in time copies, you predict the future, > knowing the time slice at which your data will be needed. Continuous > data protection is based on the premise that you don't have a clue ahead > of time which point in time you want to recover to. Essentially, for > CDP, you need to save every storage block that has ever been written, so > you can put them back in place if you so desire. > > Anyone else on the list think it is worthwhile adding CDP to the ZFS > list of capabilities? It causes space management issues, but it's an > interesting, useful idea. >
It might be interesting, but only for a limited set of applications. For applications which do things like mmap or write multiple files concurrently, I think that keeping consistency will be difficult. In the long run, you'll be better off making the applications implement their own, contextual data replication. Another sort of application which won't work well with this is one that writes an entire file for each record written. One such example is pkgadd (reason #5238 why IPS is much better than the old SVR4 packaging system). -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
