On Sep 27, 2012, at 3:24 PM, Reginald Beardsley <pulask...@yahoo.com> wrote:
> --- On Thu, 9/27/12, Richard Elling <richard.ell...@richardelling.com> wrote: > >> From: Richard Elling <richard.ell...@richardelling.com> >> Subject: Re: [OpenIndiana-discuss] Mitigating the performance impact of scrub >> To: "Discussion list for OpenIndiana" <openindiana-discuss@openindiana.org> >> Date: Thursday, September 27, 2012, 3:46 PM >> On Sep 27, 2012, at 11:51 AM, >> Reginald Beardsley <pulask...@yahoo.com> >> wrote: >> >>> Where would I find information about the kernel level >> tunable parameters? Are there specific parameters you >> have in mind? >> >> UTSL, >> http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/fs/zfs/dsl_scan.c#61 >> >> The most important tend to be: >> /etc/system settings: >> zfs:zfs_scrub_delay = 4 >> number of ticks to delay scrub >> (10ms/tick by default) >> zfs:zfs_scan_idle = 50 >> idle window size (ticks) >> >> to set on a running system, the kernel parameters are: >> zfs_scrub_delay >> zfs_scan_idle >> >> The algorithm intends to check to see if there are important >> I/Os within >> zfs_scan_idle time, and if so delay scrub I/O by >> zfs_scrub_delay. >> >>> What I'm seeing is very slow loads of >> OpenOffice. It's certainly not quick under the best of >> circumstances, but this was particularly slow. I just >> needed to read a bunch of 5-6 MB .xls files and export them >> as .csv files. >> >> If you are using HDDs, then zfs_vdev_max_pending might be >> too high. To understand >> why see: >> >> http://blog.richardelling.com/2012/03/iops-and-latency-are-not-related-hdd.html >> > > Thanks. Very useful. > > As I understand it, increasing zfs_scrub_delay and zfs_scan_idle would > throttle back the scrub so that it had less impact if other processes were > active, but would have negligible impact on scrub if the system were idle. > Is that accurate? > > Does: > > zfs_scrub_delay = 100 a bit extreme, but probably ok > zfs_scan_idle = 1000 no, you'll want to make this smaller. -- richard > > seem excessive? I'd really like the scrub to only run when I don't want the > system to do other work. > > The goal is to be able to run scrubs from cron weekly and not have it > adversely impact interactive use if I want to use the system before the scrub > finishes. If it's not interfering w/ my using the system, I'm happy to have > it take a couple of days to complete. At present it takes about 10 hours, so > if I'm working late and start a scrub just before going to bed the system is > slow when I get up. Weekly scrubs are a bit extreme. Is your hardware unreliable enough that you need to scrub weekly? -- richard -- illumos Day & ZFS Day, Oct 1-2, 2012 San Fransisco www.zfsday.com richard.ell...@richardelling.com +1-760-896-4422 _______________________________________________ OpenIndiana-discuss mailing list OpenIndiana-discuss@openindiana.org http://openindiana.org/mailman/listinfo/openindiana-discuss
