Q: Is it OK to fsfreeze --unfreeze directly after create-snapshot returns? Assume /data is the mount point for an EXT4 file system that occupies a whole EBS volume.
To create a backup, the file system is freezed and a snapshot is created.
root@ubuntu:~# fsfreeze --freeze /data
root@ubuntu:~# aws ec2 create-snapshot --volume-id vol-1234567 --description "/data snapshot"
{
    "SnapshotId": "snap-27c5ebdf",
    "Description": "/data snapshot",
    "VolumeId": "vol-1234567",
    "State": "pending",
    "VolumeSize": 250,
    "OwnerId": "744275636941",
    "StartTime": "2014-11-04T15:17:19.000Z",
    "Tags": []
}
root@ubuntu:~#

Is it at this point OK to run
root@ubuntu:~# fsfreeze --unfreeze /data

and start writing files under /data?
In other words, is it OK to start using an EBS volume directly after aws ec2 create-snapshot returns, although the state of the snapshot might be pending?

A: Yes, it is OK.
Here is a quote from
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-creating-snapshot.html
You can remount and use your volume while the snapshot status is pending.
