{"id":9213,"date":"2008-10-16T12:16:00","date_gmt":"1999-11-29T20:00:00","guid":{"rendered":"https:\/\/aidanfinn.com\/?p=9213"},"modified":"2008-10-16T12:16:00","modified_gmt":"1999-11-29T20:00:00","slug":"highly-available-hyper-v-virtual-disks","status":"publish","type":"post","link":"https:\/\/aidanfinn.com\/?p=9213","title":{"rendered":"Highly Available Hyper-V Virtual Disks"},"content":{"rendered":"<p>TONYSO <a title=\"talks \" href=\"http:\/\/blogs.technet.com\/tonyso\/archive\/2008\/10\/10\/hyper-v-how-to-plan-ha-vms.aspx\">talks <\/a>about planning VHD strategies when setting up highly available Hyper-V VM&#8217;s (using Windows clustering services).\n<\/p>\n<p>First off, MS only supports Pass Through disks and fixed size VHD&#8217;s in production so forget about using differencing disks.\n<\/p>\n<p>The VM will usually be on a LUN of it&#8217;s own.\u00a0 So you need to allocate a LUN from your cluster&#8217;s shared storage for each VM.\u00a0 (Note: Shared storage will be used in Windows Server 7 Hyper-V thanks to a new cluster file system that allows simultaneous multiple host access).\u00a0 You&#8217;ll want to save space on this LUN so you need to size it correctly.\u00a0 Here&#8217;s how I size a dedicated LUN or volume for storing a VHD:\n<\/p>\n<p><em>LUN Size = (VM RAM + VHD Size) * 1.1<\/em>\n<\/p>\n<p>This works out as:<\/p>\n<ul>\n<li>VM RAM: The amount of RAM assigned to the virtual machine, e.g. 2GB RAM.\u00a0 This is required to allow the VM to save state, e.g. during host shutdown or for quick migration.\n<\/li>\n<li>VHD Size: The amount of disk assigned to the virtual machine, e.g. 40GB.\n<\/li>\n<li>1.1: This allows for 10% free space on the volume.\u00a0 You need to allow free disk space for a healthy volume.<\/li>\n<\/ul>\n<p>Given these numbers:\n<\/p>\n<p><em>LUN Size = (2 + 40) * 1.1<\/em>\n<\/p>\n<p><em>LUN Size = 46.2GB<\/em>\n<\/p>\n<p>This figure will be rounded out as 47GB because your SAN management software probably won&#8217;t handle decimal points for the GB allocation.\n<\/p>\n<p>The VM will probably not be able to do snapshots with this calculation.\u00a0 Note that MS does not support snapshots in production &#8211; according to PSS.\u00a0 They want you to use backup tools with Hyper-V VSS support instead for state saves.\u00a0 If you do want to do snapshots then you need to allocate more disk.\u00a0 How much &#8230; who knows!\u00a0 Snapshots are done using differencing disks, e.g. anything done after the snapshot is saved in a differencing disk (hence the lack of production support from PSS?).\u00a0 This differencing disk will grow as time passes so you need to allocate disk for this.\u00a0 I&#8217;d recommend a central store for saved states.\u00a0 You can configure this on a per VM basis.\u00a0 This means the VM LUN doesn&#8217;t need to be expanded to allow for snapshots.\u00a0 Forget shrinking the VM disk if you expand it for snapshots.\u00a0 I&#8217;ve tested that with a HP EVA and it screwed up the file system\/VM.\n<\/p>\n<p><em>Credit: <\/em><a title=\"TONYSO\" href=\"http:\/\/blogs.technet.com\/tonyso\/archive\/2008\/10\/10\/hyper-v-how-to-plan-ha-vms.aspx\"><em>TONYSO<\/em><\/a><em>.<\/em>\n<\/p>\n<p>EDIT:\n<\/p>\n<p>You might want to add 5GB of disk space to the above if you want to leave room for an ISO image if using VMM 2008.\u00a0 Remember that VMM 2008 cannot share ISO&#8217;s from the library so you have to copy them &#8230; that copies them to the VM&#8217;s LUN.\u00a0 You&#8217;ll also need more space if you want to use snapshots.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>TONYSO talks about planning VHD strategies when setting up highly available Hyper-V VM&#8217;s (using Windows clustering services). First off, MS only supports Pass Through disks and fixed size VHD&#8217;s in production so forget about using differencing disks. The VM will usually be on a LUN of it&#8217;s own.\u00a0 So you need to allocate a LUN &hellip; <a href=\"https:\/\/aidanfinn.com\/?p=9213\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Highly Available Hyper-V Virtual Disks&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[20],"tags":[],"class_list":["post-9213","post","type-post","status-publish","format-standard","hentry","category-hyper-v"],"aioseo_notices":[],"jetpack_featured_media_url":"","amp_enabled":true,"_links":{"self":[{"href":"https:\/\/aidanfinn.com\/index.php?rest_route=\/wp\/v2\/posts\/9213","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/aidanfinn.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/aidanfinn.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/aidanfinn.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/aidanfinn.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=9213"}],"version-history":[{"count":0,"href":"https:\/\/aidanfinn.com\/index.php?rest_route=\/wp\/v2\/posts\/9213\/revisions"}],"wp:attachment":[{"href":"https:\/\/aidanfinn.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=9213"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/aidanfinn.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=9213"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/aidanfinn.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=9213"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}