Hi,
On 27.09.2017 16:07, Edward Napierala wrote:
2017-08-30 11:45 GMT+02:00 Eugene M. Zheganin <e...@norma.perm.ru
<mailto: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.
Yeah, but you mean dev is faster by design. So was my first thought too,
but it seems like the opposite. Default volmode is geom, and it's much
faster than dev.
Eugene.
_______________________________________________
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"
