Hi, I am sure that there are others who will answer this better, but anyway. The default replication level for files in HDFS is 3 and so most files that you see will have a replication level of 3. However when you run a Map/Reduce job the system knows in advance that every node will need a copy of certain files. Specifically the job.xml and the various jars containing classes that will be needed to run the mappers and reducers. So the system arranges that some of these files have a higher replication level. This increases the chances that a copy will be found locally. By default this higher replication level is 10.
This can seem a little odd on a cluster where you only have, say, 3 nodes. Because it means that you will almost always have some blocks that are marked under-replicated. I think that there was some discussion a while back to change this to make the replication level something like min(10, #number of nodes) However, as I recall, the general consensus was that this was extra complexity that wasn't really worth it. If it ain't broke... Hope that this helps. Peter Marron Senior Developer, Research & Development Office: +44 (0) 118-940-7609 [email protected]<mailto:[email protected]> Theale Court First Floor, 11-13 High Street, Theale, RG7 5AH, UK [cid:[email protected]] [cid:[email protected]]<https://www.facebook.com/pages/Trillium-Software/109184815778307> [cid:[email protected]]<https://twitter.com/TrilliumSW> [cid:[email protected]]<http://www.linkedin.com/company/17710> www.trilliumsoftware.com<http://www.trilliumsoftware.com/> Be Certain About Your Data. Be Trillium Certain. From: ch huang [mailto:[email protected]] Sent: 10 December 2013 01:21 To: [email protected] Subject: Re: how to handle the corrupt block in HDFS? more strange , in my HDFS cluster ,every block has three replicas,but i find some one has ten replicas ,why? # sudo -u hdfs hadoop fs -ls /data/hisstage/helen/.staging/job_1385542328307_0915 Found 5 items -rw-r--r-- 3 helen hadoop 7 2013-11-29 14:01 /data/hisstage/helen/.staging/job_1385542328307_0915/appTokens -rw-r--r-- 10 helen hadoop 2977839 2013-11-29 14:01 /data/hisstage/helen/.staging/job_1385542328307_0915/job.jar -rw-r--r-- 10 helen hadoop 3696 2013-11-29 14:01 /data/hisstage/helen/.staging/job_1385542328307_0915/job.split On Tue, Dec 10, 2013 at 9:15 AM, ch huang <[email protected]<mailto:[email protected]>> wrote: the strange thing is when i use the following command i find 1 corrupt block # curl -s http://ch11:50070/jmx |grep orrupt "CorruptBlocks" : 1, but when i run hdfs fsck / , i get none ,everything seems fine # sudo -u hdfs hdfs fsck / ........ ....................................Status: HEALTHY Total size: 1479728140875 B (Total open files size: 1677721600 B) Total dirs: 21298 Total files: 100636 (Files currently being written: 25) Total blocks (validated): 119788 (avg. block size 12352891 B) (Total open file blocks (not validated): 37) Minimally replicated blocks: 119788 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 166 (0.13857816 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 3 Average block replication: 3.0027633 Corrupt blocks: 0 Missing replicas: 831 (0.23049656 %) Number of data-nodes: 5 Number of racks: 1 FSCK ended at Tue Dec 10 09:14:48 CST 2013 in 3276 milliseconds The filesystem under path '/' is HEALTHY On Tue, Dec 10, 2013 at 8:32 AM, ch huang <[email protected]<mailto:[email protected]>> wrote: hi,maillist: my nagios alert me that there is a corrupt block in HDFS all day,but i do not know how to remove it,and if the HDFS will handle this automaticlly? and if remove the corrupt block will cause any data lost?thanks
<<inline: image001.png>>
<<inline: image002.png>>
<<inline: image003.png>>
<<inline: image004.png>>
