2017-08-30 11:45 GMT+02:00 Eugene M. Zheganin <e...@norma.perm.ru>: > Hi, > > > I have an iSCSI production system that exports a large number of zvols as > the iSCSI targets. System is running FreeBSD 11.0-RELEASE-p7 and initially > all of the zvols were confugured with default volmode. I've read that it's > recommended to use them in dev mode, so the system isn't bothered with all > of these geom structures, so I've switched all of the zvols to dev mode, > then I exported/imported the pools back. Surprisingly, the performance has > fallen down like 10 times (200-300 Mbits/sec against 3-4 Gbits/sec > previously). After observing for 5 minutes the ESXes trying to boot up, and > doing this extremely slowly, I switched the volmode back to default, then > again exported/imported the pools. The performance went back to normal. > > > So... why did this happen ? The result seems to be counter-intuitive. At > least not obvious to me.
I don't really have an answer - mav@ would be the best person to ask. Based on his description, "ZVOLs in GEOM mode don't support DPO/FUA cache control bits, had to chunk large I/Os into MAXPHYS-sized pieces and go through GEOM." There also used to be so that TRIM was only supported in the "dev" mode, but that changed a while ago. _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
