> On Jul 9, 2015, at 5:40 AM, Gabriele Bulfon <[email protected]> wrote: > > Looks like both system shows "disabled" > I used this little software : > 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]> > A: [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 > > > > 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
