Comment 67 for bug 1470250

Thanks @f-bosch for your clarification in #62. So my understanding is: the (temporary) I/O downgrade during the period of backup might be caused by the fact the disk space has been almost used up (?) recently, but it also might be somehow related to the backup. Let's focus on the backup issue at present.

Thanks @jsalisbury for the detailed test steps & script!
I suppose the result in #66 implies a real issue, which can't be fixed by the patches mentioned in bug 1519917. We're going to further investigate the issue too with the help of your test script.