2009/8/10 Bob Friesenhahn <[email protected]>: > On Sun, 9 Aug 2009, Kaya Bekirolu wrote: >> >> The last time I did a quick-and-dirty check, I found >> that OpenSolaris and ZFS could make "better" use of the slog for NFSv3 >> commits, but they don't. Consider the following sequential write >> sequence: >> >> 1. NFS WRITE 0-32K (32K) >> 2. NFS WRITE 32K-64K (32K) >> 3. NFS WRITE 64K-96K (32K) >> 4. COMMIT 0-96K >> >> It is only at step 4 that any data is sent to the slog, which doesn't make >> very efficient use of the device. You could imagine an alternative >> approach > > Only synchronous writes make into into the slog and until the NFS COMMIT, > there has not been any synchronous write. > > For best performance with zfs and its default 128K block size, you would > want to do the NFS commit after accumulating (at least) 128K of data to > write. > > Also, SSD devices often need to erase much more data than even 128K (e.g. > 512K) in order to prepare for a write so three writes may take much more > time than one large write. SSD devices write large blocks at a time so if a
Recent SSDs typically accumulate (coalesce) multiple writes in the on-board DRAM to flush these to NAND at a later time, so multiple writes are hardly an issue. Regards, Andrey > portion of the block is updated, then existing block data needs to be copied > into SSD RAM, updated, and then written to a fresh (erased) block. > > Bob > -- > Bob Friesenhahn > [email protected], http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > _______________________________________________ > storage-discuss mailing list > [email protected] > http://mail.opensolaris.org/mailman/listinfo/storage-discuss > _______________________________________________ storage-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/storage-discuss
