I saw something stranger. the size of backup json file became much less at 8.30 12:59. maybe a core dump happened at that upgrade.
restore failed with these two json : default-20140902T114827-version_upgrade.json or default-20140830T045915-version_upgrade.json
restore success with this json: default-20140827T130619-key_import.json
restore with this file block the client with very long time, until now, it's still block: default-20140830T045740-version_upgrade.json
alt@alt-ThinkPad-T430s $ ls -lt
总用量 940
-rw-r--r-- 1 alt alt 247295 9月 2 19:48 default-20140902T114827-version_upgrade.json
-rw-r--r-- 1 alt alt 247295 8月 30 12:59 default-20140830T045915-version_upgrade.json
-rw-r--r-- 1 alt alt 458342 8月 30 12:57 default-20140830T045740-version_upgrade.json
-rw-r--r-- 1 alt alt 2361 8月 27 21:06 default-20140827T130619-key_import.json