今天，当我在尝试组建Hyper-V Cluster的时候，进行到Cluster Configuration检查的时候，检查结果中有一项Fail：Validate SCSI-3 Persistent Reservation（如图）

详细的报告中还有进一步的错误提示：

Failed to read PR on cluster disk 0 from node HyperV1.lab.local. Some PR implementations fail to report existing PR on a disk.
Cluster Disk 0 does not support Persistent Reservation.
http://byfiles.storage.msn.com/y1pQq8acLktiIKnf91Sl-l-aYKqjj5FTdhaE90eMHr1iL-REE-NyK9j7c0LplOsgS4t?PARTNER=WRITERPersistent Reservation (PR)" />
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那么什么是SCSI-3 PR呢？

Symantec的解释
（https://vias.symantec.com/docportal/sf/5.0/hpux/html/vcs_users/ch_vcs_communications11.html）

SCSI-3 Persistent Reservation (SCSI-3 PR) supports device access from multiple systems, or from multiple paths from a single system. At the same time it blocks access to the device from other systems, or other paths.

VCS logic determines when to online a service group on a particular system. If the service group contains a disk group, the disk group is imported as part of the service group being brought online. When using SCSI-3 PR, importing the disk group puts registration and reservation on the data disks. Only the system that has imported the storage with SCSI-3 reservation can write to the shared storage. This prevents a system that did not participate in membership arbitration from corrupting the shared storage.

SCSI-3 PR ensures persistent reservations across SCSI bus resets.

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Note Use of SCSI 3 PR protects against all elements in the IT environment that might be trying to write illegally to storage, not only VCS related elements.
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IBM这样解释
（http://publib.boulder.ibm.com/infocenter/clresctr/vxrx/index.jsp?topic=/com.ibm.cluster.rsct_5300_06.vsd.doc/bl506_undperr.html）
Persistent Reserve refers to a set of Small Computer Systems Interface-3 (SCSI-3) standard commands and command options which provide SCSI initiators with the ability to establish, preempt, query, and reset a reservation policy with a specified target device. The functionality provided by the Persistent Reserve commands is a superset of the reserve/release commands. The Persistent Reserve commands are not compatible with the legacy reserve/release mechanism, and target devices can only support reservations from either the legacy mechanism or the new mechanism. Attempting to mix Persistent Reserve commands with legacy reserve/release commands will result in the target device returning a reservation conflict error

总之，SCSI-3 PR就是一组SCSI命令集，用在多个系统访问一个共享存储的时候协调之用。并且于旧的命令集不兼容。Windows 2008用SCSI-3 PR，而Windows 2003用SCSI-2。当Windows 2003访问SCSI-3的共享存储的时候，会发生错误，MS KB911030解释了这个bug，http://support.microsoft.com/kb/911030


参考文档
1) What are SCSI reservations?
https://now.netapp.com/Knowledgebase/solutionarea.asp?id=kb29190
你需要一个NOW帐号来访问上述页面。


20081218注：经过实验，找到了问题就是因为NAS设备版本太老的缘故。当NetApp NAS设备升级到DATAONTAP 7.2.5以后版本，创建LUN格式就可以选择windows_2008，此时支持SCSI-3 PR。类似的问题也发生在测试时使用了不支持SCSI-3的NAS，比如nas模拟器 freenas等。