Adding to Harsh's comments: You can also tweak a few OS level parameters to improve the I/O performance. 1) Mount the filesystem with "noatime" option. 2) Check if changing the IO scheduling the algorithm will improve the cluster's performance. (Check this file /sys/block/<device_name>/queue/scheduler) 3) If there are lots of I/O requests and your cluster hangs because of that, you can increase the queue length by increasing the value in /sys/block/<device_name>/queue/nr_requests.
-----Original Message----- From: Harsh J [mailto:[email protected]] Sent: Sunday, April 28, 2013 12:03 AM To: <[email protected]> Subject: Re: High IO Usage in Datanodes due to Replication They seem to be transferring blocks between one another. This may most likely be due to under-replication and the NN UI will have numbers on work left to perform. The inter-DN transfer is controlled by the balancing bandwidth though, so you can lower that down if you want to, to cripple it - but you'll lose out on time for a perfectly replicated state again. On Sat, Apr 27, 2013 at 11:33 PM, selva <[email protected]> wrote: > Hi All, > > I have lost amazon instances of my hadoop cluster. But i had all the > data in aws EBS volumes. So i launched new instances and attached volumes. > > But all of the datanode logs keep on print the below lines it cauased > to high IO rate. Due to IO usage i am not able to run any jobs. > > Can anyone help me to understand what it is doing? Thanks in advance. > > 2013-04-27 17:51:40,197 INFO > org.apache.hadoop.hdfs.server.datanode.DataNode: > DatanodeRegistration(10.157.10.242:10013, > storageID=DS-407656544-10.28.217.27-10013-1353165843727, > infoPort=15075, > ipcPort=10014) Starting thread to transfer block > blk_2440813767266473910_11564425 to 10.168.18.178:10013 > 2013-04-27 17:51:40,230 INFO > org.apache.hadoop.hdfs.server.datanode.DataNode: > DatanodeRegistration(10.157.10.242:10013, > storageID=DS-407656544-10.28.217.27-10013-1353165843727, > infoPort=15075, ipcPort=10014):Transmitted block > blk_2440813767266473910_11564425 to > /10.168.18.178:10013 > 2013-04-27 17:51:40,433 INFO > org.apache.hadoop.hdfs.server.datanode.DataNode: Receiving block > blk_2442656050740605335_10906493 src: /10.171.11.11:60744 dest: > /10.157.10.242:10013 > 2013-04-27 17:51:40,450 INFO > org.apache.hadoop.hdfs.server.datanode.DataNode: Received block > blk_2442656050740605335_10906493 src: /10.171.11.11:60744 dest: > /10.157.10.242:10013 of size 25431 > > Thanks > Selva > > > > > > -- Harsh J
