{"action":"created","issue":{"url":"https://api.github.com/repos/zfsonlinux/zfs/issues/3127","labels_url":"https://api.github.com/repos/zfsonlinux/zfs/issues/3127/labels{/name}","comments_url":"https://api.github.com/repos/zfsonlinux/zfs/issues/3127/comments","events_url":"https://api.github.com/repos/zfsonlinux/zfs/issues/3127/events","html_url":"https://github.com/zfsonlinux/zfs/issues/3127","id":58530926,"number":3127,"title":"Crash with SCST + ZFS + IOmeter","user":{"login":"kpande","id":5016187,"avatar_url":"https://avatars.githubusercontent.com/u/5016187?v=3","gravatar_id":"","url":"https://api.github.com/users/kpande","html_url":"https://github.com/kpande","followers_url":"https://api.github.com/users/kpande/followers","following_url":"https://api.github.com/users/kpande/following{/other_user}","gists_url":"https://api.github.com/users/kpande/gists{/gist_id}","starred_url":"https://api.github.com/users/kpande/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kpande/subscriptions","organizations_url":"https://api.github.com/users/kpande/orgs","repos_url":"https://api.github.com/users/kpande/repos","events_url":"https://api.github.com/users/kpande/events{/privacy}","received_events_url":"https://api.github.com/users/kpande/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":4,"created_at":"2015-02-23T00:31:51Z","updated_at":"2015-02-23T05:12:09Z","closed_at":null,"body":"Some people here say \"SCST brings out the worst in ZFS\" but I am wondering if it is poorly written or simply using some kind of functionality that IET does not use.\r\n\r\nI started testing SCST because it is hailed as a mythical beast in the Linux iSCSI world, supporting features the more basic IET or even COMSTAR don't - one of these claims includes 'higher performance'.\r\n\r\nI began testing using my regular i7, 32GB, 4x2TB WD Black box\r\n\r\ntest: boot a Windows 8.1 image from iSCSI over 1gbe and run latest IOmeter (as of today)\r\n* 64kb block size\r\n* 32 IO per burst\r\n* 80% random, 20% sequential\r\n* 90% write, 10% read\r\n* 8 workers\r\n\r\n\r\nSCST:\r\n\r\n- starts at 750 IOPS and climbs to 1800 and then tanks back to 800 IOPS over 8 minutes\r\n- system crash and becomes unresponsive. I tried to unload SCST but ZFS still blocked in zr_wr_iss\r\n\r\nIET:\r\n\r\n- starts at 1200 IOPS, climbs to 2100 and stays there\r\n\r\n\r\nimage of server-side stats: http://tripleback.net/public/scst-iet.png\r\n\r\nThe red rectangle is the area where SCST is tested and the green rectangle is IET test results. The sharp drop-off is because my stats failed to collect any data while SCST hung the box. You can see IET clearly pushes 3k IOPS and uses the same net I/O.\r\n\r\nWhat's going on here?"},"comment":{"url":"https://api.github.com/repos/zfsonlinux/zfs/issues/comments/75490470","html_url":"https://github.com/zfsonlinux/zfs/issues/3127#issuecomment-75490470","issue_url":"https://api.github.com/repos/zfsonlinux/zfs/issues/3127","id":75490470,"user":{"login":"kpande","id":5016187,"avatar_url":"https://avatars.githubusercontent.com/u/5016187?v=3","gravatar_id":"","url":"https://api.github.com/users/kpande","html_url":"https://github.com/kpande","followers_url":"https://api.github.com/users/kpande/followers","following_url":"https://api.github.com/users/kpande/following{/other_user}","gists_url":"https://api.github.com/users/kpande/gists{/gist_id}","starred_url":"https://api.github.com/users/kpande/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/kpande/subscriptions","organizations_url":"https://api.github.com/users/kpande/orgs","repos_url":"https://api.github.com/users/kpande/repos","events_url":"https://api.github.com/users/kpande/events{/privacy}","received_events_url":"https://api.github.com/users/kpande/received_events","type":"User","site_admin":false},"created_at":"2015-02-23T05:12:09Z","updated_at":"2015-02-23T05:12:09Z","body":"Sorry, I should have been more clear about what it means to have tested revisions 159 to 220 - the kmem rework was introduced somewhere arond 175 and this crash occurred with my pre-kmem code."}}