Question regarding relevance of syncer(4) in the context of ZFS

[Paul]

10 August 2018, 17:39:52, by "Konstantin Belousov" <kostikbel at gmail.com>:

> On Fri, Aug 10, 2018 at 05:28:11PM +0300, Paul wrote:
> > Hello team,
> > 
> > 
> > If my understanding is correct then ZFS does not need to be pushed around and being told when to sync data to devices.
> > It is perfectly capable of keeping data consistent and synchronized according to configured options.
> > 
> > We even disable 'sync' option of file system that we use. But unfortunately we see a constant and periodical spikes 
> > of load on our servers that are directly related to wake-ups of 'syncer' kernel daemon. Is it safe to assume that
> > 'syncer' is not necessary on configurations that only use ZFS, and no other file systems? And hence, is it safe
> > to assume that setting all of 'kern.filedelay', 'kern.dirdelay' and 'kern.metadelay' to some large values will not 
> > compromise system's durability?
> 
> One of the job of the syncer is to convert dirty user-mapped pages into
> the filesystem-specific write requests.  Without syncer touching the mount
> point, corresponding pages could linger forever, or at least until a memory
> pressure causes pagedaemon to clean them.


Thanks a lot for clarification! I didn't think about dirty user-mapped pages...

Best regards,
Paul