{"id":725,"date":"2010-04-07T06:54:00","date_gmt":"2010-04-07T06:54:00","guid":{"rendered":"\/blogs\/paul\/post\/A-SQL-Server-DBA-myth-a-day-(730)-multiple-mirrors-and-log-shipping-load-delays.aspx"},"modified":"2017-04-13T12:47:40","modified_gmt":"2017-04-13T19:47:40","slug":"a-sql-server-dba-myth-a-day-730-multiple-mirrors-and-log-shipping-load-delays","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/paul\/a-sql-server-dba-myth-a-day-730-multiple-mirrors-and-log-shipping-load-delays\/","title":{"rendered":"A SQL Server DBA myth a day: (7\/30) multiple mirrors and log shipping load delays"},"content":{"rendered":"<p>(Look in the <a href=\"https:\/\/www.sqlskills.com\/blogs\/paul\/category\/misconceptions\/\">Misconceptions<\/a> blog category for the rest of the month&#8217;s posts and check out the 60-page PDF with all the myths and misconceptions blog posts collected together when you join our <a href=\"https:\/\/www.sqlskills.com\/join-the-sqlskills-insider-community\/\" target=\"_blank\">Insider list<\/a>, plus my online <a href=\"https:\/\/www.pluralsight.com\/courses\/sqlserver-myths\" target=\"_blank\">Myths and Misconceptions training course<\/a> on Pluralsight.)<\/p>\n<p>\n<font face=\"verdana,geneva\" size=\"2\">A short one today as I&#39;m teaching a class on HA strategies and technologies for Microsoft DBAs on the Redmond campus, so let&#39;s make it an appropriate topic:<\/font>\n<\/p>\n<p>\n<font face=\"verdana,geneva\"><font size=\"2\"><strong>Myth #7:<\/strong> <em>A database can have multiple mirrors.<\/em><\/font><\/font>\n<\/p>\n<p>\n<strong><u><em><font face=\"verdana,geneva\" size=\"2\">FALSE<\/font><\/em><\/u><\/strong>\n<\/p>\n<p>\n<font face=\"verdana,geneva\" size=\"2\">This one&#39;s pretty cut and dried &#8211; database mirroring only allows a single mirror of a principal database. If you want to have extra copies of the principal database, consider using log shipping. You can have as many log shipping secondaries as you want.<\/font>\n<\/p>\n<p>\n<font face=\"verdana,geneva\" size=\"2\">One other cool thing about log shipping is that you can have one of the secondaries set to have a load delay of, say, 8 hours. This means the log backups taken on the principal (don&#39;t you love it that the various technologies have different nomenclature:<\/font>\n<\/p>\n<ul>\n<li>\n<div>\n\t<font face=\"verdana,geneva\" size=\"2\">database mirroring: principal &#8211; mirror<\/font>\n\t<\/div>\n<\/li>\n<li>\n<div>\n\t<font face=\"verdana,geneva\" size=\"2\">log shipping: primary&nbsp; &#8211; secondary<\/font>\n\t<\/div>\n<\/li>\n<li>\n<div>\n\t<font face=\"verdana,geneva\" size=\"2\">replication: publisher &#8211; subscriber<\/font>\n\t<\/div>\n<\/li>\n<\/ul>\n<p>\n<font face=\"verdana,geneva\" size=\"2\">Ok &#8211; this parenthetical clause kind-of got a life of it&#39;s own&#8230;) won&#39;t be restored on the log shipping secondary until 8 hours have passed. If someone drops a table in production, it will pretty much immediately get dropped in the mirror (with whatever delay the SEND and WAIT queues have at the time &#8211; but you can&#39;t *stop it*) but the log shipping secondary with the load delay will still have it intact.<\/font>\n<\/p>\n<p>\n<font face=\"verdana,geneva\" size=\"2\">Incidentally, the SQLCAT team wrote a really good article debunking the myth (which stems from Books Online) that you can only mirror 10 databases per instance &#8211; see <\/font><a href=\"http:\/\/blogs.msdn.com\/b\/sqlcat\/\"><font face=\"verdana,geneva\" size=\"2\">Mirroring a Large Number of Databases in a Single SQL Server Instance<\/font><\/a><font face=\"verdana,geneva\" size=\"2\">. Also take a look at the KB article I wrote for CSS last year which discusses the same thing: <\/font><a href=\"https:\/\/support.microsoft.com\/kb\/2001270\"><font face=\"verdana,geneva\" size=\"2\">KB 2001270 Things to consider when setting up database mirroring in SQL Server<\/font><\/a><font face=\"verdana,geneva\" size=\"2\">.<\/font>\n<\/p>\n<p>\n<font face=\"verdana,geneva\"><br \/>\n<font size=\"2\"><\/font><\/font>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>(Look in the Misconceptions blog category for the rest of the month&#8217;s posts and check out the 60-page PDF with all the myths and misconceptions blog posts collected together when you join our Insider list, plus my online Myths and Misconceptions training course on Pluralsight.) A short one today as I&#39;m teaching a class on [&hellip;]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32,46,58,61],"tags":[],"class_list":["post-725","post","type-post","status-publish","format-standard","hentry","category-database-mirroring","category-high-availability","category-log-shipping","category-misconceptions"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>A SQL Server DBA myth a day: (7\/30) multiple mirrors and log shipping load delays - Paul S. 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