> When you have a striped storage device under a > file system, then the database or file system's view > of contiguous data is not contiguous on the media.
Right. That's a good reason to use fairly large stripes. (The primary limiting factor for stripe size is efficient parallel access; using a 100 MB stripe size means that an average 100 MB file gets less than two disks' worth of throughput.) ZFS, of course, doesn't have this problem, since it's handling the layout on the media; it can store things as contiguously as it wants. > There are many different ways to place the data on the media and we would > typically > strive for a diverse stochastic spread. Err ... why? A random distribution makes reasonable sense if you assume that future read requests are independent, or that they are dependent in unpredictable ways. Now, if you've got sufficient I/O streams, you could argue that requests *are* independent, but in many other cases they are not, and they're usually predictable (particularly after a startup period). Optimizing for the predicted access cases makes sense. (Optimizing for observed access may make sense in some cases as well.) -- Anton This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
