> On Jul 9, 2015, at 12:56 PM, Gabriele Bulfon <[email protected]> wrote: > > But the main question is: why does it work differently on the zfs side? > 2012 kernel just sasy "ok, no sync, no zil, just run as fast as hell" > 2014 kernel somewhat understands and start syncing anyway, using zil
The default mode for comstar targets changed from write-cache-enabled to write-cache-disabled. Since the cache is in RAM, this is more reliable from a data protection perspective. This has always been a tunable on both the initiator and target side, as it is part of the SCSI spec. -- richard > > > > Da: Richard Elling <[email protected]> > A: [email protected] > Data: 9 luglio 2015 19.44.27 CEST > Oggetto: Re: [discuss] iscsi sync=standard changed? > > > >> On Jul 9, 2015, at 5:40 AM, Gabriele Bulfon <[email protected] >> <mailto:[email protected]>> wrote: >> >> Looks like both system shows "disabled" >> I used this little software : >> http://milek.blogspot.it/2010/02/zvols-write-cache.html >> <http://milek.blogspot.it/2010/02/zvols-write-cache.html> >> >> What makes me worried now is that I discovered that 2012 kernel is NEVER >> using zil (used zilstat) on iscsi vols with sync=standard, as if the system >> is using RAM for caching because those vol are fast as hell! > > This is how disk drives work. SCSI is nominally an async protocol: the > initiator is responsible for > flushing the target's cache (see also NFS async writes+commit). Most modern > file systems and > databases properly issue cache sync requests to maintain consistency. > >> >> Instead, the new kernel uses zil with sync=standard, but looks too slow >> behind two 10GB ethernets. > > The default setting for nonvolatile cache in the target is disabled (wcd = > true).? > This means all writes to LUs are, by default, committed to persistent storage > before ack. > > Again, the initiator can change this policy using SCSI commands. > >> >> I'm starting to get really confused... >> Does it means I should set sync=always on older kernel to force those iscsi >> to sync on zil? > > No. Manage this through the SCSI target or initiator. > ?-- richard > >> In this case I will go down to the performances of the new kernel? >> >> >> >> ---------------------------------------------------------------------------------- >> >> Da: Yuri Pankov <[email protected] <mailto:[email protected]>> >> A: [email protected] <mailto:[email protected]> >> Data: 8 luglio 2015 19.33.28 CEST >> Oggetto: Re: [discuss] iscsi sync=standard changed? >> >> On Wed, 8 Jul 2015 16:18:58 +0200 (CEST), Gabriele Bulfon wrote: >> > Hi, >> > >> > I think I've found why an April 2012 kernel shows faster response on >> > iscsi than a Dec 2014 one. >> > Looks like the iscsi sync=standard works almost like disabled on the old >> > one, while almost like enabled on the new one. >> > >> > Obviously, justs by adding the zil to the new one will let the iscsi >> > work as expected. >> > I was just trying to guess why the two systems were acting different on >> > the same config without zil. >> > >> > So, my question is: >> > - is the sync=standard of iscsi vols changed since Apr 2012, so now it >> > syncs much more than before? >> > - can I be safe on installed machines with old kernel, where iscsi-vols >> > have sync=default, syncing less, but having a zil? >> >> This commit *could* be related, check if the wcd settings of your ZFS >> volumes differ between the systems: >> >> https://github.com/illumos/illumos-gate/commit/7e0955bbb1c326d78038afe0d108c8ae4934a78a >> >> <https://github.com/illumos/illumos-gate/commit/7e0955bbb1c326d78038afe0d108c8ae4934a78a> >> >> >> > > illumos-discuss | Archives > <https://www.listbox.com/member/archive/182180/=now> > <https://www.listbox.com/member/archive/rss/182180/21175743-23d1427b> | > Modify <https://www.listbox.com/member/?&;> Your Subscription > <http://www.listbox.com/> ------------------------------------------- illumos-discuss Archives: https://www.listbox.com/member/archive/182180/=now RSS Feed: https://www.listbox.com/member/archive/rss/182180/21175430-2e6923be Modify Your Subscription: https://www.listbox.com/member/?member_id=21175430&id_secret=21175430-6a77cda4 Powered by Listbox: http://www.listbox.com
