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CIS 212
Microcomputer
Architecture
Day 26
Rhys Eric Rosholt
Office:
Office Phone:
Web Site:
Email Address:
Gillet Hall - Room 304
718-960-8663
http://comet.lehman.cuny.edu/rosholt/
rhys.rosholt @ lehman.cuny.edu
Chapter 12
File and Secondary Storage
Management
Chapter 12
File and Secondary Storage
Management
Chapter Outline
File-Management Systems
Directory Content and Structure
Storage Allocation
File Manipulation
Access Controls
Focus – Windows NTFS
File Migration, Backup, and Recovery
Focus – RAID
Storage Consolidation
Chapter Goals
• Describe the components and functions of a file
management system
• Compare the logical and physical organization of
files and directories
• Explain how secondary storage locations are
allocated to files and describe the data structures
used to record those allocations
• Describe file manipulation operations, including
open, close, read, delete, and undelete operations
• List access controls that can be applied to files
and directories
• Describe security, backup, recovery, and fault
tolerance methods and procedures
• Compare and contrast storage area networks and
network-attached storage
Chapter 12
Topics
File Management Systems
• Collection of system software that manages
all aspects of user and program access to
secondary storage
• Usually part of the operating system
• Translates operations into commands to
physical storage devices
• Implemented in four layers (command layer,
file control, storage I/O control, and
secondary storage devices)
Operating System
Layers vs.
File Management
System Layers
Bridges between logical and physical
views of secondary storage
Allocates secondary storage locations
to individual files and directories
Includes software modules for device
drivers for each storage device or
device controller, interrupt handlers,
buffers and cache managers
Logical and Physical
Storage Views
• Logical view
– Collection of files organized within
directories and storage volumes
• Physical view
– Collection of physical storage locations
organized as a linear address space
Typical Logical and Physical
Secondary Storage
Logical Structure of a Data File
The file is subdivided into multiple records and
each record is composed of multiple fields.
File Content and Type
• FMS supports limited number of file types:
– Executable programs
– Operating system commands
– Textual or unformatted binary data
• Modern FMSs can define new file types and
install utility programs to manipulate them
(file association)
File Types
• Normally declared when a file is created
and:
– Stored within a directory, or
– Declared through a filename convention
• Determine:
– Physical organization of data items and
data structures within secondary storage
– Operations that may be performed upon
the file
– Filename restrictions
Registered
File Types
Windows XP
Association Details
of a File Type in Windows XP
Directory Content and Structure
A directory contains information
about files and subdirectories
•
•
•
•
•
•
•
name
file type
location
size
ownership
access controls
time stamps
Hierarchical Directory Structure
• Directories can contain other directories,
creating a tree structure, but cannot be
contained within more than one parent
• Ways that names of access paths can be
specified:
– Complete path (fully qualified reference)
– Relative path
• Each storage device has a root directory
Hierarchical Directory Structure
Active
(working)
directory
Graph Directory Structure
• More flexible than hierarchical directory
structure
– Files and subdirectories can be contained
within multiple directories
– Directory links can form a cycle
Graph Directory Structure
Storage Allocation
• Secondary storage devices
– Large number of storage locations
– Low frequency of allocation changes
– Divided into allocation units
Allocation Units
• Smallest number of secondary storage bytes
that can be allocated to a file; cannot be
smaller than unit of data transfer between
storage device and controller (block)
• Assigned/reclaimed by FMS as files and
directories are created or expanded/shrink
or are deleted
• Size difficult to change once set
Allocation Unit Size
• Tradeoffs
– Efficient use of secondary storage space
for files
– Size of storage allocation data structures
– Efficiency of storage allocation
procedures
• Smaller units
– More efficient use of storage space
• Larger units
– Allow smaller storage allocation data
structures
Storage Allocation Tables
• Data structures that record which allocation
units are free and which belong to files
• Format and content vary across FMSs
• Can contain linked lists in simpler FMSs or
indices or other complex data structures in
more complex FMSs
Storage Blocks Allocated to
Three Files
Directory Content
for the Three Files
Free allocation units are assigned
to a hidden system file called
SysFree
Storage Allocation Table
for the Three Files
All of a file allocation’s units are “chained” together
in sequential order by a series of pointers.
Blocking
• Logical record grouping within physical
records
• Described by a numeric ratio of logical
records to physical records (blocking factor)
Blocking of Logical Records
into Physical Records
Blocking
factor =
4:3
Blocking
factor =
2:3
Buffering
• Temporary storage of data as it moves
between programs and secondary storage
devices
– Physical records are stored in the buffer
as they are read from secondary storage
– FMS extracts logical records from
buffers and copies them to data area of
the application program
• Each buffer is the size of one allocation unit
• Improves I/O performance if enough are
used
Input from Secondary Storage
to an Application Using a Buffer
File Manipulation
• Exact set of service layer functions varies
among FMSs, but typically includes create,
copy, move, delete, read, and write
• Application programs interact directly with
FMS through OS service layer
• Users interact indirectly with FMS through
command layer
NTFS MFT Records
File Open and Close Operations
• File open
– Causes FMS to find the file, verify
access privileges, allocate buffers, and
update internal table of open files
• File close
– Causes FMS to flush buffer content to
the storage device, release buffers,
update file time stamps, and update table
of open files
Delete and Undelete Operations
• Delete
– Does not immediately remove files; some
content remains on secondary storage unit
all allocation units have been reassigned
and overwritten
– File content can be visible to intruders
• Undelete
– Can be used to reconstruct directory and
storage allocation table contents
Access Controls
• Granted by file owners and system
administrators for reading, writing, and
executing files
• Provide security at the expense of additional
FMS overhead
File Migration,
Backup, and Recovery
• Provided by most FMSs to protect files
against damage or loss
File Migration
(Version Control)
• Automatic storage and backup of old file
versions
• Balances storage cost of each file version
with anticipated user demand for that
version
Batch Account
Transaction Update
Original
Updated Copy
File Backup
• Protects against data loss (file content,
directory content, and storage allocation
tables)
• Store backup copies on a different storage
device in a different physical location
• Manual or automatic
• Full or incremental
Transaction Logging
• Automatically records all changes to file
content and attributes in a separate storage
area; also writes them to the file’s I/O
buffer
• Provides high degree of protection against
data loss due to program or hardware failure
• Imposes a performance penalty; used only
when costs of data loss are high
File Recovery
• Automated and manual components
• Can search backup logs for copies of lost or
damaged files
• Can perform consistency checking and repair
procedures for crashed system or physically
damaged storage device
Fault Tolerance
• Methods of securing file content against
hardware failure
– File backup
– Recovery
– Transaction logging
– Mirroring
– RAID
• “Redundant Array of Inexpensive Disks”
Mirroring
• All disk write operations are made
concurrently to two different storage
devices
• Provides high degree of protection against
data loss with no performance penalty if
implemented in hardware
• Disadvantages
– Cost of redundant disk drives
– Higher cost of disk controllers that
implement mirroring
RAID
• Disk storage technique that improves
performance and fault tolerance
• All levels except RAID 1 use data striping
– Breaks a unit of data into smaller
segments and stores them on multiple
disks
• Multiple levels can be layered to combine
their best features (e.g. RAID 10)
• Can be implemented in hardware or software
RAID Levels
Data Striping
Each segment is written in parallel to a separate disk.
RAID Write
If the parity disk fails,
the other disks still retain their original data bits.
RAID 10
Mirrors individual disks (RAID 1),
then stripes data (RAID 0) across multiple mirrored pairs.
Storage Consolidation
• Overcomes inefficiencies of direct-attached
storage (DAS) in multiple-server
environments
• Common approaches
– Storage area network (SAN)
– Network-attached storage (NAS)
Storage Consolidation
Storage Area Network
(SAN)
• High-speed interconnection
among general-purpose servers
and one or more storage
servers
• Block-oriented access
• Common in multi-server
environments with mainframes
or supercomputers and
substantial overlap among
server storage needs
• Expensive to purchase and
administer, but avoid costs of
duplicate storage and storage
administration
Network-Attached Storage
(NAS)
• Dedicated to managing one or
more file systems
• Accessed by other servers and
clients over a local or wide area
network
• File-oriented access
• Common when geographically
dispersed servers need access
to a common file system
• Cheaper to acquire than SAN,
but at the price of lower
performance
Server Cluster with SAN
Server Cluster with NAS
Summary
File management systems
Directory content and structure
Storage allocation
File manipulation
Access controls
File migration, backup, and recovery
Storage consolidation
Chapter Goals
• Describe the components and functions of a file
management system
• Compare the logical and physical organization of
files and directories
• Explain how secondary storage locations are
allocated to files and describe the data structures
used to record those allocations
• Describe file manipulation operations, including
open, close, read, delete, and undelete operations
• List access controls that can be applied to files
and directories
• Describe security, backup, recovery, and fault
tolerance methods and procedures
• Compare and contrast storage area networks and
network-attached storage
Next Class
Thursday
May 10, 2012
Rhys Eric Rosholt
Office:
Office Phone:
Web Site:
Email Address:
Gillet Hall - Room 304
718-960-8663
http://comet.lehman.cuny.edu/rosholt/
rhys.rosholt @ lehman.cuny.edu