'ZFS optimizes random writes versus potential sequential reads.'Now I don't think the current readahead code is where we want it to be yet but, in the same way that enough concurrent 128K I/O can saturate a disk (I sure hope that Milkowski's data will confirm this, otherwise I'm dead), enough concurrent read I/O will do the same. So It's a simple matter of programming to detect file sequential access an issue enough I/Os early enough. With UFS, we had a simple algorithm and one tunable. Touch 2 sequential page, read a cluster ahead. Then, don't do any other I/O until all the data is processed. This is flawed in many respect. And it certainly requires large cluster size to get good I/O throughput because it had stop and go behavior. With ZFS (again, prefetch code being looked upon), I think we can manage get good I/O throughput using 128K, through enough concurrency and intelligent coding. -r _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
