> eric kustarz wrote: > > On Jul 9, 2007, at 11:21 AM, Scott Lovenberg wrote: > > > > > >> You sir, are a gentleman and a scholar! > Seriously, this is exactly > > the information I was looking for, thank you very > much! > >> > >> Would you happen to know if this has improved > since build 63 or if > >> chipset has any effect one way or the other? > >> > > > > Naw. Without having information on how exactly the > controller/disk > > firmware really works, we're merely speculating > that the firmware is > > where the problem is. Getting that information > from the disk vendors > > is <ahem> tricky. > > > > Unfortunately, testing has not support the theory > that the problem is with > the controller hardware, driver, disk or disk > firmware. So far every > valid measurement with using FPDMA READ/WRITE (NCQ) > v. READ/WRITE > DMA EXT. has shown anywhere from less that 1% > improvement using NCQ > to up to 22% improvement. The biggest improvements > are seen > when the disk caches are disabled, but I have > measured up to 19% improvement > w.r.t. time spent waiting for I/Os to complete with > the caches enabled. > > More investigation is needed. > > > > Absolutely more investigation is needed. > > eric
Just a thought or two off the top of my head; is the caching daemon (bdflush or something to that effect) on when you are performing these tests. I think it flushes every 20 or 30 seconds by default, IIRC? I'm not sure, but this sounds like a buffering thing where it's waiting for a full buffer to flush the changes. Are these disks in ATA/DMA/UDMA/PIO, SATA, or SCSI interfaces? Are these disks Western Digitals, I've heard their caching algorithms aren't optimized at all (strictly heresy). It could be a delay on the channel if it's PATA and the other drive on the channel is being accessed... Perhaps this is a cache coherency problem (is the arch. x86, IA1/2, SPARC, PPC... single or SMP... memory timings?)? This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
