Re: [Xen-API] Move blktap2.reset_leaf call to new SR command "epoch_begin"

[Rushikesh Jadhav <2rushikeshj@xxxxxxxxx>]

On Tuesday, November 27, 2012, Mike McClurg <mike.mcclurg@xxxxxxxxxx> wrote:
> On 27/11/12 16:04, Rushikesh Jadhav wrote:
>> On Tue, Nov 27, 2012 at 9:24 PM, Mike McClurg <mike.mcclurg@xxxxxxxxxx

>> <mailto:mike.mcclurg@xxxxxxxxxx>> wrote:
>>
>>     On 27/11/12 15:44, Rushikesh Jadhav wrote:
>>     > Hi Mike and Andrei,
>>     >
>>     > Thanks for making the discussion open about this famous issue.
>>     >
>>     > Many times we face this issue. If a host is hang then the VMs from
>>     that
>>     > host are unable to boot on any other host until the database VDI

>>     RW flag
>>     > is reset. Usual error is "The VDI is already attached in RW mode".
>>      The
>>     > solution procedure is to reboot the hang host or resetvdis manually.

>>     >
>>     > If we can do on-boot=reset then this will help to quickly boot failed
>>     > VMs on new host without errors. As mentioned this will apply to start
>>     > and restart operation but will "xe vm-reset-powerstate" be affected ?

>>     >
>>     > Regards,
>>     > Rushikesh
>>
>>     Hi Rushikesh,
>>
>>     I don't think that on-boot=reset does what you think it does. Setting

>>     on-boot=reset on a VDI will force it to "reset" on attach, meaning that
>>     it will delete the leaf node of the VHD tree that makes up the VDI.
>>
>>     Basically, this is a feature which lets you create a VM which will roll

>>     its disks back to a specified state every time you reboot. All of the
>>     writes that you made to the disk before the reboot (and after setting
>>     on-boot=reset) will be gone.
>>

>>     The problem is that there is a bug where this action happens on VM
>>     migrate! This is what we're trying to fix.
>>
>>     Mike
>>
>>
>> Thank for the further info. So are you making a magic RO VDI which can

>> hold the writes till its attached  ?
>> That sounds good to me :)
>>
>> Do you think that there is any usefulness to what I thought about
>> on-boot=reset ?
>
> Well, I think it would be very unsafe, because you'd basically be

> working around the locking mechanism for the VDIs. Using resetvdis
> manually is safer.
>
> Mike
>

Thanks Mike.
I'm sorry for hijacking the thread, I'll try to get this in a new thread with more details.

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