HADOOP-14557. Document HADOOP-8143 (Change distcp to have -pb on by default). Contributed by Bharat Viswanadham.

Author: jojochuang

hadoop-tools/hadoop-distcp/src/site/markdown/DistCp.md.vm

@@ -217,7 +217,7 @@ Command Line Options
 
 Flag              | Description                          | Notes
 ----------------- | ------------------------------------ | --------
-`-p[rbugpcaxt]` | Preserve r: replication number b: block size u: user g: group p: permission c: checksum-type a: ACL x: XAttr t: timestamp | When `-update` is specified, status updates will **not** be synchronized unless the file sizes also differ (i.e. unless the file is re-created). If -pa is specified, DistCp preserves the permissions also because ACLs are a super-set of permissions. The option -pr is only valid if both source and target directory are not erasure coded.
+`-p[rbugpcaxt]` | Preserve r: replication number b: block size u: user g: group p: permission c: checksum-type a: ACL x: XAttr t: timestamp | When `-update` is specified, status updates will **not** be synchronized unless the file sizes also differ (i.e. unless the file is re-created). If -pa is specified, DistCp preserves the permissions also because ACLs are a super-set of permissions. The option -pr is only valid if both source and target directory are not erasure coded. **Note:** If -p option's are not specified, then by default block size is preserved.
 `-i` | Ignore failures | As explained in the Appendix, this option will keep more accurate statistics about the copy than the default case. It also preserves logs from failed copies, which can be valuable for debugging. Finally, a failing map will not cause the job to fail before all splits are attempted.
 `-log <logdir>` | Write logs to \<logdir\> | DistCp keeps logs of each file it attempts to copy as map output. If a map fails, the log output will not be retained if it is re-executed.
 `-m <num_maps>` | Maximum number of simultaneous copies | Specify the number of maps to copy data. Note that more maps may not necessarily improve throughput.