On Feb 19, 2010, at 8:35 AM, Edward Ned Harvey wrote: > One more thing I’d like to add here: > > The PERC cache measurably and significantly accelerates small disk writes. > However, for read operations, it is insignificant compared to system ram, > both in terms of size and speed. There is no significant performance > improvement by enabling adaptive readahead in the PERC. I will recommend > instead, the PERC should be enabled for Write Back, and have the readahead > disabled. Fortunately this is the default configuration on a new perc > volume, so unless you changed it, you should be fine. > > It may be smart to double check, and ensure your OS does adaptive readahead. > In Linux (rhel/centos) you can check that the “readahead” service is loading. > I noticed this is enabled by default in runlevel 5, but disabled by default > in runlevel 3. Interesting. > > I don’t know how to check solaris or opensolaris, to ensure adaptive > readahead is enabled.
ZFS has intelligent prefetching. AFAIK, Solaris disk drivers do not prefetch. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
