David Dyer-Bennet wote: > Sure, if only a single thread is ever writing to the > disk store at a time. > > This situation doesn't exist with any kind of > enterprise disk appliance, > though; there are always multiple users doing stuff.
Ok, I'll bite. Your assertion seems to be that "any kind of enterprise disk appliance" will always have enough simultaneous I/O requests queued that any sequential read from any application will be sufficiently broken up by requests from other applications, effectively rendering all read requests as random. If I follow your logic, since all requests are essentially random anyway, then where they fall on the disk is irrelevant. I might challenge a couple of those assumptions. First, if the data is not fragmented, then ZFS would coalesce multiple contiguous read requests into a single large read request, increasing total throughput regardless of competing I/O requests (which also might benefit from the same effect). Second, I am unaware of an enterprise requirement that disk I/O run at 100% busy, any more than I am aware of the same requirement for full network link utilization, CPU utilization or PCI bus utilization. What appears to be missing from this discussion is any shred of scientific evidence that fragmentation is good or bad and by how much. We also lack any detail on how much fragmentation does take place. Let's see if some people in the community can get some real numbers behind this stuff in real world situations. Cheers, Marty -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
