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Forum Discussion
Windows "Dynamic Disks" and iSCSI. Why you shouldn't.
Disclaimer: These problems apply to software iSCSI, not hardware host bus adapters.
As people may have noticed, this is a rather sensitive issue. Microsoft's "dynamic disk" layout subsystem has the habit of offlining a disk if there is a SINGLE failed read or write detected. And herein lies part of the problem.
During bootup, the disk services starts a lot earlier than the IP stack, meaning the disk services have ample time to get errors before there is an IP stack to reach the iSCSI target over. With Windows 2008 things get a little better, since the "is the device still there?" check is placed later in the boot, giving IP a chance to start. If the device _AND_ it's persistent reservation is still valid it may work. May. May not.
There are tricks to making microsofts iSCSI software bypass this by using rather undocumented registry keys. These keys aren't available in the GUI for a reason. They tell the iSCSI stack to keep onlining a disk as long as it is reachable, something that might mask an actual problem with your target such as data corruption.
//Svein
As people may have noticed, this is a rather sensitive issue. Microsoft's "dynamic disk" layout subsystem has the habit of offlining a disk if there is a SINGLE failed read or write detected. And herein lies part of the problem.
During bootup, the disk services starts a lot earlier than the IP stack, meaning the disk services have ample time to get errors before there is an IP stack to reach the iSCSI target over. With Windows 2008 things get a little better, since the "is the device still there?" check is placed later in the boot, giving IP a chance to start. If the device _AND_ it's persistent reservation is still valid it may work. May. May not.
There are tricks to making microsofts iSCSI software bypass this by using rather undocumented registry keys. These keys aren't available in the GUI for a reason. They tell the iSCSI stack to keep onlining a disk as long as it is reachable, something that might mask an actual problem with your target such as data corruption.
//Svein
4 Replies
- would you provide that reg key to fix that issue, please ? I have similar case with W2k8 server + iscsi + 9 Tb Lun.
- I think you have the solution for the same problem a few of my clients are having, getting them to change from Dynamic disks is going to be a problem though!
Could you please post the reg key fix. - Does this also apply to NICs which provide iSCSI offload functionality (for example NIC with broadcom 5709 chipsets)? Does a NIC with iSCSI offload engine qualify as compatible hardware iSCSI HBA for use of dynamic disks in Windows Server 2008R2?
- Just use vmware with iSCSI and a VM with dynamic disks and your problem is solved!
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