OK, what are the major changes?<\/p>\n
There IS NO Redirected IO in WS2012 CSV Backup<\/span><\/strong><\/p>\n Let me restate that in another way: Windows Server 2012 does not use<\/em> Redirected IO to backup CSVs.<\/p>\n This has been made possible thanks to substantial changes in how VSS places VMs that are stored on CSV into a quiescent state.\u00a0 The backup agent (VSS Requestor) kicks off a backup request with a list of virtual machines.\u00a0 The Hyper-V Writer identifies the storage location(s) of the VMs\u2019 files.\u00a0 A new component, the CSV Writer, is responsible for coordinating the Hyper-V nodes in the cluster \u2026 meaning all VMs on a CSV that is being backed up to be placed into a quiescent state at the same time.\u00a0 This allows for a single distributed VSS snapshot of each CSV.\u00a0 That allows the provider (hardware, software or system) to go to work and get the snapshot.<\/p>\n This is much<\/em> simpler than what CSV did in Windows Server 2008 R2.\u00a0 [The following does not happen in WS2012] There was no CSV Writer.\u00a0\u00a0\u00a0 There was no coordination, so Redirected IO was required.\u00a0 The node performing a snapshot needed exclusive access to the volume so all IO went through it for the time being.\u00a0 A lot of people knew that bit up to there.\u00a0 The bit that most people didn\u2019t know was that each node (hosting VMs that were being backed up) took snapshots of each CSV that was being backed up.\u00a0 And that<\/em> could cause problems.<\/p>\n I\u2019ve heard several times now from people who\u2019ve experienced issues with volumes going offline during backup.\u00a0 There were two causes that I\u2019ve seen, and both were related to a third party hardware VSS provider:<\/p>\n But, all that is G-O-N-E <\/em>when backing up CSV on Windows Server 2012:<\/p>\n SCSI3 Reservation Starvation Should Go Away<\/span><\/strong><\/p>\n Every node in a Hyper-V cluster used SCSI3 persistent reservations and SCSI3 reservations to connected to CSVs.\u00a0 Every SAN has a finite number of those persistent reservations and reservations.\u00a0 The SCSI3 persistent reservations was a bottleneck.\u00a0 No manufacturer shares that number, and it\u2019s a hell of a lot smaller than you’d expect \u2013 we typically find out about it during a support call.\u00a0 To compound this, each host required a number of SCSI3 persistent reservations, and that multiplied based on:<\/p>\n What happens when you deploy too many nodes, CSVs, or storage channels?\u00a0 CSVs go offline.\u00a0 Yup.\u00a0 The SAN is starved of resources to connect the hosts to the LUNs.\u00a0 I saw this with small deployments with an entry level SAN, 3 hosts, and 5 CSVs.\u00a0 And it aint pretty.<\/p>\n Imagine a cluster with 64 nodes!?!?!\u00a0 With Windows Server 2012, each node gets a static key instead of using the legacy persistent reservation multiplication.\u00a0 That means your SAN can support more CSVs and more hosts running Windows Server 2012 than it would have with Windows Server 2008 R2.\u00a0 Note that the static key is assigned when the node is added to the cluster.<\/p>\n You can find the static keys in the registry of your cluster nodes in HKEY_LOCAL_MACHINEClusterNodes<Node Number>ReserveID (REG_QWORD).\u00a0 You can identify which node number is which host by the NodeName (REG_SZ) value.\u00a0 You can see an example of this below.<\/p>\n This new system, which replaces persistent reservations, gives you better cluster infrastructure scalability, but it doesn\u2019t eliminate the scalability limits of your SAN.<\/p>\n Microsoft made lots of changes with CSV 2.0 in Windows Server 2012.\u00a0 But it seems like that message has not gotten through to people.\u00a0 I\u2019ve responded to quite a few comments here on the blog and I\u2019m seeing stuff on forums.\u00a0 What\u2019s really annoying is that when you tell people that X has changed, they … Continue reading “The Big Changes In WS2012 Cluster Shared Volume (CSV)”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"_wpcom_ai_launchpad_first_post":false,"footnotes":""},"categories":[20],"tags":[55,63,181,99,195,118],"class_list":["post-14083","post","type-post","status-publish","format-standard","hentry","category-hyper-v","tag-backup","tag-failover-clustering","tag-hyper-v","tag-storage","tag-virtualisation","tag-windows-server-2012"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t![\"image\"](\"https:\/\/aidanfinn.com\/wp-content\/uploads\/2013\/01\/image_thumb25.png\" "\\"image\\"")
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