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https://issues.apache.org/jira/browse/HDFS-11361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15935395#comment-15935395
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Anu Engineer commented on HDFS-11361:
-------------------------------------

[~vagarychen] Thanks for taking care of this. Overall the patch looks very 
good, some minor comments below.

* CBlockConfigKeys.java: nit: typos
-- line: 73: long => log
-- line: 74: useful to doing  => useful for doing 
-- line: 89: background i/O. => I/O.
-- line: 111: comment seems to be wrong.

* CBlockStorageImpl.java
{code}  
@Override
public void close() throws IOException {
if (cache instanceof CBlockLocalCache) {
     try {
        cache.close();
         } catch (IllegalStateException ise) {
       LOGGER.error("Not able to shutdown cache since we have dirty blocks.");
       throw ise;
    }
  }
}
{code}
-- we don't need the if check if the cache instanceof
-- LOGGER.error message seems incorrect.

* Pipeline.java 
{code}
  public void setData(byte[] data) {
    this.data = Arrays.copyOf(data, data.length);
  }
 {code}
 -- check if data is null before getting length, same comment for other 
functions that got added.

> Block Storage : add cache interface
> -----------------------------------
>
>                 Key: HDFS-11361
>                 URL: https://issues.apache.org/jira/browse/HDFS-11361
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs
>            Reporter: Chen Liang
>            Assignee: Chen Liang
>         Attachments: HDFS-11361-HDFS-7240.001.patch, 
> HDFS-11361-HDFS-7240.002.patch, HDFS-11361-HDFS-7240.003.patch, 
> HDFS-11361-HDFS-7240.004.patch, HDFS-11361-HDFS-7240.005.patch
>
>
> This JIRA includes two major pieces: 1. the interface exposed to upper layer 
> operating system that mounts the file system; and 2. the interface exposed to 
> lower layer container storage layer.
> On one hand, to make CBlock mountable and accessible for a POSIX OS, we need 
> to implement file system protocol. We chose to do this by running cblock with 
> jSCSI (http://jscsi.org/) which is a java implementation of iSCSI protocol. 
> More specifically, CBlock volume will exposed as an java-based iSCSI target, 
> and any machine that has iSCSI installed will be able to talk to CBlock 
> volume and mounted locally just as any disks. This is JIRA make a starting 
> point by introducing jSCSI and implementing its {{IStorageModule}}. This will 
> be registered to jSCSI server in future JIRA. 
> One the other hand, to be able to have the CBlock talk to container layer 
> with better performance, CBlock should be able to cache data locally. More 
> specifically, clients' read/write should be performed on the locally disk 
> cache, while threads are pushing and retrieving data in backend. This JIRA 
> takes the first step by defining interfaces for the local cache. 



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