Alluxio Monthly Webinar | Cloud-Native Model Training on Distributed Data
Access Methods and File System Mounting.pptx
1. Access Methods
• Computer stores many files.
• Applications are used to access files.
• Three ways to access files:
- Sequential access method.
- Direct access method.
- Index access method.
2. Sequential Access Method:
• Serial Access.
• Information in the file is processed in order, one record after the
other.
• Operations:
- Read_next();
- Write_next();
- Rewind();
• For example, editors and compilers, audio or video cassette.
3. Direct Access Method:
• The file is viewed as a numbered sequence of blocks or records.
• Thus, we may read block 14, then read block 53, and then write block
7.
• Operations:
- Read(n);
- Write(n);
- Goto(n);
• E.g Database System.
4. Index Access Method:
• We first search the index and then use the pointer to access the file
directly and to find the desired record.
• The primary index file contains the contains the pointer to secondary
index file.
• Secondary index file contains the actual index of the block of the file.
5. File-System Mounting
• A file must be opened before it is used.
• File system must be mounted before it can be available to processes
on the system.
• Mount point—the location within the file structure where the file
system is to be attached.
• Typically, a mount point is an empty directory.
6.
7.
8. File-System Mounting
• For e.g external storage media (e.g CDROM and Floppy disk) are
usually mounted in subdirectory of the /mnt directory(i.e
/mnt/cdrom and /mnt/floppy).
• The mac OS X operating system searches for a file system on the
device. If it finds one, it automatically mounts the file system under
the /volumes directory, adding a folder icon labeled with the name of
the file system (as stored in the device directory).
• In some systems, like UNIX, the mount commands are explicit. A
system configuration file contains a list of devices and mount points
for automatic mounting at boot time, but other mounts may be
executed manually.
