Rebalance is slow when indexing/compaction and query load are going on in parallel

Cluster information:
- 8 centos 6.2 64bit server with 4 cores CPU
- Each server has 32 GB RAM and 400 GB SSD disk.
- SSD disk format ext4 on /data
- Each server has its own drive, no disk sharing with other server.
- Cluster has 2 buckets, default (11GB) and saslbucket (11GB) with consistent view enable. For 2 buckets, we use only 68% total RAM of system.
- Load 12 million items to saslbucket and 45 million items to default bucket. Each key has size from 512 bytes to 1500 bytes
- Each bucket has one doc and 2 views for each doc (default d1 and saslbucket d11)

* Create cluster with 4 nodes installed couchbase server 2.0.0-1746

10.6.2.37
10.6.2.38
10.6.2.39
10.6.2.40

* Data path /data
* View path /data

* Let load running at 6K ops, query 400 to 500 per second
* Add 4 nodes to cluster and rebalance
10.6.2.42
10.6.2.43
10.6.2.44
10.6.2.45

* rebalance hang. Filed bug MB-6706
* Try rebalance again. Cluster rebalances saslbucket first and took 9 hours to complete rebalance saslbucket
* default bucket took 32 hours to complete

Link to collect_info of all nodes https://s3.amazonaws.com/packages.couchbase/collect_info/orange/2_0_0/201209/8nodes-col-info-1746-reb-slow-constn-enable-20120925-141314.tgz

Each atop file size from 1.5 GB to 2.5 GB. If atop file needed, I will upload them as request