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Chapter 24. Grid File System

Red Hat Data Grid’s GridFileSystem is an experimental API that exposes an Red Hat Data Grid-backed data grid as a file system.

Warning

This is an experimental API. Use at your own risk.

Specifically, the API works as an extension to the JDK’s File , InputStream and OutputStream classes: specifically, GridFile, GridInputStream and GridOutputStream. A helper class, GridFilesystem, is also included.

Essentially, the GridFilesystem is backed by 2 Red Hat Data Grid caches - one for metadata (typically replicated) and one for the actual data (typically distributed). The former is replicated so that each node has metadata information locally and would not need to make RPC calls to list files, etc. The latter is distributed since this is where the bulk of storage space is used up, and a scalable mechanism is needed here. Files themselves are chunked and each chunk is stored as a cache entry, as a byte array.

Here is a quick code snippet demonstrating usage: 

Cache<String,byte[]> data = cacheManager.getCache("distributed");
Cache<String,GridFile.Metadata> metadata = cacheManager.getCache("replicated");
GridFilesystem fs = new GridFilesystem(data, metadata);

// Create directories
File file=fs.getFile("/tmp/testfile/stuff");
fs.mkdirs(); // creates directories /tmp/testfile/stuff

// List all files and directories under "/usr/local"
file=fs.getFile("/usr/local");
File[] files=file.listFiles();

// Create a new file
file=fs.getFile("/tmp/testfile/stuff/README.txt");
file.createNewFile();
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Copying stuff to the grid file system: 

InputStream in=new FileInputStream("/tmp/my-movies/dvd-image.iso");
OutputStream out=fs.getOutput("/grid-movies/dvd-image.iso");
byte[] buffer=new byte[20000];
int len;
while((len=in.read(buffer, 0, buffer.length)) != -1) out.write(buffer, 0, len);
in.close();
out.close();
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Reading stuff from the grid: 

InputStream in=in.getInput("/grid-movies/dvd-image.iso");
OutputStream out=new FileOutputStream("/tmp/my-movies/dvd-image.iso");
byte[] buffer=new byte[200000];
int len;
while((len=in.read(buffer, 0, buffer.length)) != -1) out.write(buffer, 0, len);
in.close();
out.close();
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24.1. WebDAV demo
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Red Hat Data Grid ships with a demo WebDAV application that makes use of the grid file system APIs. This demo app is packaged as a WAR file which can be deployed in a servlet container, such as JBoss AS or Tomcat, and exposes the grid as a file system over WebDAV. This could then be mounted as a remote drive on your operating system.

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