On Tue, 8 Mar 2011, Edward Ned Harvey wrote:
That's my argument, unless somebody can tell me where my logic is wrong. Disk write cache offers zero benefit. And disk read cache only offers benefit in unusual cases that I would call esoteric.
I was agreeing with your email until it came to this conclusion. When zfs writes a transaction group, it sends data to the disks, and then tells all the disks involved in the transaction to flush their write cache. The disk write cache helps with the step where data is sent to the disks since it is much faster to write into the disk write cache than to write to the media. Besides helping with unburdening the I/O channel, disks are already commiting data in their write cache prior to recieving the cache sync request. Having more disks actively writing to disk at once results in better parallel behavior.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
