mapred.local.dir overwritten automatically by Task Tracker

Version: Hadoop 2.0.0-cdh4.3.0

First I mounted mapred.local.dir (/opt/var/mapred/local/1) on local disk. The disk soon got filled up.
After I softlink /opt/var/mapred/local/1 to SAN, everything ran fine for a day. Later, somehow the softlink was removed and Task Tracker process created a directory again as /opt/var/mapred/local/1 on local disk again by itself.

Quesiton:
1. What is disk quota requirement for mapred.local.dir?
2. How often mapred.local.dir get a cleanup?
2. Does Task Tracker automatically switch mapred.local.dir to local disk?

FYI - local disk is used now. I did create softlink 1 -> /opt/var/hadoop/dfs/dn/1/mapred.tmp, but the soft link was removed.
$ pwd
/opt/var/mapred/local/1
$ ls -al
total 20
drwxrwxr-x. 5 mapred hadoop 4096 Sep 15 23:02 .
drwxrwxr-x. 3 mapred hadoop 4096 Sep 15 05:48 ..
drwxr-xr-x. 5 mapred mapred 4096 Sep 16 04:39 taskTracker
drwxr-xr-x. 3 mapred mapred 4096 Sep 15 23:02 ttprivate
drwxr-xr-x. 20 mapred mapred 4096 Sep 16 05:49 userlogs

SAN location for mapred.local.dir (softlinked)
$ pwd
/opt/var/hadoop/dfs/dn/1/mapred.tmp
$ ls -al
total 28
drwxr-xr-x. 7 mapred hadoop 4096 Sep 13 23:44 .
drwxrwxr-x. 5 hdfs hdfs 4096 Sep 13 23:12 ..
drwxr-xr-x. 3 mapred mapred 4096 Sep 14 22:53 taskTracker
drwxr-xr-x. 2 mapred mapred 4096 Sep 13 23:44 toBeDeleted
drwxr-xr-x. 2 mapred mapred 4096 Sep 13 23:44 tt_log_tmp
drwx------. 3 mapred mapred 4096 Sep 14 22:53 ttprivate
drwxr-xr-x. 9 mapred mapred 4096 Sep 14 23:04 userlogs