root fs is full while iSCSI mounted

[kiserp]

CentOS release 6.6 (Final)
2.6.32-504.8.1.el6.x86_64
We had problem like this ones.

I've faced with that problem once again.
System blocks write operations, because disk is full, df shows its 100% used, but de facto it is not, there should be more than half free space.
After remount of iscsi disk df shows right disk usage.

Can someone tell me what should I do to avoid this problem henceforth?

[TrevorH]

I moved your post to the CentOS 6 forum since it's clear from your kernel version that is what you are running.

You almost certainly have a process running that has deleted files but still has them open. When this happens the space used by those files is not released until the process closes them or ends. Running lsof | grep -i del should show you all files that are deleted but still open and you can use that list to discover the culprit.