Try adding the following to /boot/loader.conf and reboot: hw.mpt.enable_sata_wc=1
The default value, -1, instructs the driver to leave the STA drives at their configuration default. Often times this means that the MPT BIOS will turn off the write cache on every system boot sequence. IT DOES THIS FOR A GOOD REASON! An enabled write cache is counter to data reliability. Yes, it helps make benchmarks look really good, and it's acceptable if your data can be safely thrown away (for example, you're just caching from a slower source, and the cache can be rebuilt if it gets corrupted). And yes, Linux has many tricks to make this benchmark look really good. The tricks range from buffering the raw device to having 'dd' recognize the requested task and short-circuit the process of going to /dev/null or pulling from /dev/zero. I can't tell you how bogus these tests are and how completely irrelevant they are in predicting actual workload performance. But, I'm not going to stop anyone from trying, so give the above tunable a try and let me know how it works. Btw, I'm not subscribed to the hackers mailing list, so please redistribute this email as needed. Scott >________________________________ > From: Dieter BSD <dieter...@gmail.com> >To: freebsd-hackers@freebsd.org >Cc: mja...@freebsd.org; gi...@freebsd.org; sco...@freebsd.org >Sent: Thursday, January 17, 2013 9:03 PM >Subject: Re: IBM blade server abysmal disk write performances > >> I am thinking that something fancy in that SAS drive is >> not being handled correctly by the FreeBSD driver. > >I think so too, and I think the something fancy is "tagged command queuing". >The driver prints "da0: Command Queueing enabled" and yet your SAS drive >is only getting 1 write per rev, and queuing should get you more than that. >Your SATA drive is getting the expected performance, which means that NCQ >must be working. > >> Please let me know if there is anything you would like me to run on the >> BSD 9.1 system to help diagnose this issue? > >Looking at the mpt driver, a verbose boot may give more info. >Looks like you can set a "debug" device hint, but I don't >see any documentation on what to set it to. > >I think it is time to ask the driver wizards why TCQ isn't working, >so I'm cc-ing the authors listed on the mpt man page. > > > _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
