On Fri, 25 Sep 2009, Ross Walker wrote:
As a side an slog device will not be too beneficial for large sequential writes, because it will be throughput bound not latency bound. slog devices really help when you have lots of small sync writes. A RAIDZ2 with the ZIL spread across it will provide much
Surely this depends on the origin of the large sequential writes. If the origin is NFS and the SSD has considerably more sustained write bandwidth than the ethernet transfer bandwidth, then using the SSD is a win. If the SSD accepts data slower than the ethernet can deliver it (which seems to be this particular case) then the SSD is not helping.
If the ethernet can pass 100MB/second, then the sustained write specification for the SSD needs to be at least 100MB/second. Since data is buffered in the Ethernet,TCP/IP,NFS stack prior to sending it to ZFS, the SSD should support write bursts of at least double that or else it will not be helping bulk-write performance.
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
