Great answers, Richard :) and thanks a lot. But....what if the SCSI initiator is VMware? I read that he's going async as default... Da: Richard Elling 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] 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 | Modify Your Subscription
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