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A comment on AWS vs. GCP reliability is wildly different. Parent comment

Re:AWS vs. GCP reliability is wildly different by pclmulqdq on Wednesday September 21, 2022 @05:52PM (#32932026)
They pause your VM, copy everything about its state over to the new machine, and quickly start the other instance. It's pretty clever. I think there are tricks you can play with machines that have large memory footprints to copy most of it before the pause, and only copy what has changed since then during the pause.

The disks are all on the network, so no need to move anything there.

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Re:AWS vs. GCP reliability is wildly different by prmoustache on Wednesday September 21, 2022 @06:12PM (#32932253)
In reality it sync the memory first to the other host and only pause the vm when the last state sync is small enough to be so quick the pause is barely measurable.
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Re:AWS vs. GCP reliability is wildly different by water-your-self on Wednesday September 21, 2022 @06:21PM (#32932349)
Indian jones and the register states
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Re:AWS vs. GCP reliability is wildly different by lbhdc on Wednesday September 21, 2022 @06:28PM (#32932413)
When its transferring the state to the target, how does it handle memory updates that are happening at that time? Is the programs execution paused at that point?
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Re:AWS vs. GCP reliability is wildly different by GauntletWizard on Wednesday September 21, 2022 @07:12PM (#32932855)
No, but the memory accesses have hooks that say "This memory was written". Then, program execution is paused, and just the sections of memory that were written are copied again.

This has memory performance characteristics - I ran a benchmark of memory read/write speed while this was happening once. It more than halved memory speed for the 30s or so it took from migration started to migration complete. The pause, too, was much longer.

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Re:AWS vs. GCP reliability is wildly different by lbhdc on Wednesday September 21, 2022 @07:37PM (#32933070)
Ahh I think that was the piece I was missing, thanks! I didn't realize there were hooks for tracking memory changes.
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Re:AWS vs. GCP reliability is wildly different by outworlder on Wednesday September 21, 2022 @07:09PM (#32932824)
No, they keep track of dirty pages.
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