android.os下的StatFs类主要用来获取文件系统的状态，能够获取sd卡的大小和剩余空间，获取系统内部空间也就是/system的大小和剩余空间等等。
看下读取sd卡的：
Java代码
void readSDCard() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
File sdcardDir = Environment.getExternalStorageDirectory();
StatFs sf = new StatFs(sdcardDir.getPath());
long blockSize = sf.getBlockSize();
long blockCount = sf.getBlockCount();
long availCount = sf.getAvailableBlocks();
Log.d("" , "block大小:" + blockSize+ ",block数目:" + blockCount+ ",总大小:" +blockSize*blockCount/ 1024 + "KB" );
Log.d("" , "可用的block数目：:" + availCount+ ",剩余空间:" + availCount*blockSize/ 1024 + "KB" );
}
}
void readSDCard() {
String state = Environment.getExternalStorageState();
if(Environment.MEDIA_MOUNTED.equals(state)) {
File sdcardDir = Environment.getExternalStorageDirectory();
StatFs sf = new StatFs(sdcardDir.getPath());
long blockSize = sf.getBlockSize();
long blockCount = sf.getBlockCount();
long availCount = sf.getAvailableBlocks();
Log.d("", "block大小:"+ blockSize+",block数目:"+ blockCount+",总大小:"+blockSize*blockCount/1024+"KB");
Log.d("", "可用的block数目：:"+ availCount+",剩余空间:"+ availCount*blockSize/1024+"KB");
}
} 然后看下读取系统内部空间的：
Java代码
void readSystem() {
File root = Environment.getRootDirectory();
StatFs sf = new StatFs(root.getPath());
long blockSize = sf.getBlockSize();
long blockCount = sf.getBlockCount();
long availCount = sf.getAvailableBlocks();
Log.d("" , "block大小:" + blockSize+ ",block数目:" + blockCount+ ",总大小:" +blockSize*blockCount/ 1024 + "KB" );
Log.d("" , "可用的block数目：:" + availCount+ ",可用大小:" + availCount*blockSize/ 1024 + "KB" );
}
void readSystem() {
File root = Environment.getRootDirectory();
StatFs sf = new StatFs(root.getPath());
long blockSize = sf.getBlockSize();
long blockCount = sf.getBlockCount();
long availCount = sf.getAvailableBlocks();
Log.d("", "block大小:"+ blockSize+",block数目:"+ blockCount+",总大小:"+blockSize*blockCount/1024+"KB");
Log.d("", "可用的block数目：:"+ availCount+",可用大小:"+ availCount*blockSize/1024+"KB");
} StatFs获取的都是以block为单位的，这里我解释一下block的概念：
1.硬件上的 block size, 应该是"sector size"，linux的扇区大小是512byte
2.有文件系统的分区的block size, 是"block size"，大小不一，可以用工具查看
3.没有文件系统的分区的block size，也叫“block size”，大小指的是1024 byte
4.Kernel buffer cache 的block size, 就是"block size"，大部分PC是1024
5.磁盘分区的"cylinder size"，用fdisk 可以查看。
我们这里的block size是第二种情况，一般SD卡都是fat32的文件系统，block size是4096.
这样就可以知道手机的内部存储空间和sd卡存储空间的总大小和可用大小了。