The write cache decouples the actual write to disk from the data transfer from the host. For a streaming operation, this means that the disk can typically stream data onto tracks with almost no latency (because the cache can aggregate multiple I/O operations into full tracks which can be written without waiting for the right sector to come around).
Disks could do this with "write cache disabled" if they actually used their write cache anyway and simply didn't acknowledge the write immediately, but it appears they don't, perhaps because this would add extra latency compared to actually waiting for the disk to get to the right place and transferring the data (well, one track's worth at least), or perhaps because SATA disks are normally used with the write cache enabled and hence that's the optimized code path. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
