Outline

Fundamental of Hard Disk „ Interfaces ‰ IDE, ATA, PATA, SATA, SCSI, SAS Drive Technology (7) „ File Systems

‰ FAT, NTFS

Assistant Prof. Piya Kovintavewat, Ph.D. Data Storage Technology Research Unit Nakhon Pathom Rajabhat University

E-mail: [email protected] URL: http://home.npru.ac.th/piya SCILAB: http://home.npru.ac.th/piya/webscilab

Parallel ATA / IDE „ To reduce the overall PC Host system cost, Western Digital developed the ATAPI (ATA Packet Interface) „ Advanced Technology Attachment (ATA) is a standard specifications in 1995 interface for connecting storage devices ‰ Allow additional types of storage devices to be attached ‰ E.g., HDDs and CD-ROM drives inside personal computers to the IDE bus

„ IDE is short for “Integrated Drive Electronics”, ‰ Use PATA bus to connect non-hard drives peripherals sometimes called Parallel ATA (PATA) ‰ Support CD-ROM, CD-Writer, DVD/CD-Writer combo drives in every personal computer ‰ Originally developed as a joint effort between Western Digital (1986) and several key computer industry players

‰ Parallel ATA or IDE is controlled through the industry standard ATA Specifications Parallel ATA Review

„ Cable lengths up to only 18 inches (46 centimeters)

„ Primary storage for desktop and notebook PCs

„ Backward compatible with all previous versions Two motherboard ATA connectors „ ATA6 – supports up to 100 MB/s ATA connector „ ATA7 is the most current revision

„ 16-bit parallel data bus

„ 16 control signals

„ 40 pin connector – 80-conductor cable

Parallel ATA / IDE Cable Disadvantages of Parallel ATA

„ Maximum cable length should not exceed 18” „ High Pin Count – 40 pin connection

„ The second connector stub should be no more than 6” from the end „ High Voltage – PATA requires 5V tolerant buffers, which „ If only one drive is connected, it should be connected to the impose integration problems with new silicon processes physical end of the cable „ Cable Problems – Flat ribbon cable can interfere with airflow HOSTDRIVE 1 DRIVE 0 and cooling with maximum 18” length

„ Performance Issues – Data transfer rates of greater than 100 or 133 MB/s would require the implementation of technological enhancements that would no longer be 6” max. backward compatible

„ Superseded by Serial ATA (2003) 18” max. Serial ATA (SATA)

„ SATA is a computer bus designed for transfer of data between a computer and mass storage devices such as hard disk drives and optical drives.

‰ Communicate over a high-speed serial cable

„ Advantages of SATA over PATA

‰ Faster data transfer First generation (1.5 Gbit/s) A 7-pin Serial ATA data cable ‰ Ability to remove or add devices while operating (hot swapping) SATA ports on a motherboard ‰ Thinner cables that let air cooling work more efficiently

‰ More reliable operation with tighter data integrity checks „ SATA was designed as a successor to the ATA standard ‰ Expected to eventually replace the older technology (i.e., PATA)

Advantages of SATA over PATA Serial ATA Cable and Connectors

„ Low Pin Count ⇒ 4 pin connection „ Transmit and Receive 1.5 Gb/s serial stream = 150 MB/s

„ Point-to-point protocol ⇒ No Master/Slave concept „ Handle minor data rate frequency variation via Spread „ Low Voltage Requirement Spectrum Clocking (SSC) to improve EMI emissions from

‰ SATA requires only 500mV peak-to-peak to support new silicon cable processes „ Data CRC Checking for all bursts across cable for added „ Better Cabling data integrity

‰ Thinner cable allows for better airflow and cooling „ Cables & connectors specifications

‰ Longer 1 meter cable lengths allowed ‰ Specified SATA connector location, size, pin definition, etc.

„ Software Compatibility ‰ Cable length is 0 – 1 meter

‰ SATA is a drop-in replacement for PATA ‰ 1 transmit pair & 1 receive pair – low voltage differential pairs Serial ATA Connector SATA Data and Power Pin Definitions

SATA Power Connector SATA Data Connector

Same connector defined for 2.5”, 3.5”, and 5.25” Drives

3.5” Serial ATA Transition into PCs is Slow Serial ATA is Moving Into SCSI Territories

60 Serial ATA in Enterprise Shift Away from Traditional 14 Enterprise Interfaces

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Source: TrendFOCUS, April 2004 Small Computer System Interface (SCSI) „ SCSI is a peripheral interface

‰ Up to 8 or 16 devices can be attached to a single bus „ A set of standards for physically connecting and „ SCSI is a peer to peer interface transferring data between computers and peripheral devices. ‰ Define communication from host to host, host to a peripheral device, peripheral device to a peripheral device. ‰ Define commands, protocols, and electrical and optical interfaces. „ Currently, SCSI is popular on high-performance

„ Most commonly used for workstations and servers. HDDs and tape drives „ Desktop computers and notebooks more typically use

‰ Can connect a wide range ‰ ATA/IDE or SATA interfaces for HDDs

of other devices, including ‰ USB, e-sata, and FireWire connections for external devices scanners and CD drives.

Serial Attached SCSI (SAS) Comparison

„ The first SCSI interface was parallel SCSI (or SPI) „ SCSI offers transfer rates higher than SATA

‰ Use a parallel electrical bus design ‰ More complex bus ⇒ higher manufacturing cost

„ As of 2008, SPI is being replaced by SAS „ SCSI buses allow connection of several drives (using multiple channels, 7 or 15 on each channel) ‰ Use a serial point-to-point design but retains other aspects of the technology (still use SCSI commands) ‰ SATA allows one drive per channel (unless using a port multiplier) „ SCSI drives provide greater sustained throughput than SATA „ The SAS is a new generation serial communication drives because of disconnect-reconnect and aggregating protocol for devices performance. ‰ Designed to allow for much higher speed data transfers „ SCSI and SAS drives are typically more expensive ‰ Compatible with SATA ‰ Usually used in servers and disk arrays „ SATA devices are normally compatible with SAS enclosures and adapters

‰ SCSI devices cannot be directly connected to a SATA bus

„ ATA and SATA drives ⇒ Inexpensive and used in the home computer market

„ Generally, HDD has a low failure rate because of increased quality of its heads, platters and supporting manufacturing processes, not because of having a certain interface.

File Allocation Table (FAT) FAT Overview

„ The most simplistic of the file systems „ The FAT file system is a table that resides at the very "top" of the volume. ‰ Used in DOS, Windows 9x, and NT ‰ To protect the volume, two copies of the FAT are kept in case „ Examples: one becomes damaged (FAT1 and FAT2)

‰ FAT1: The first copy of the FAT ‰ The FAT tables and the root directory must be stored in a fixed location ‰ FAT2: The second copy of the FAT „ A disk formatted with FAT is allocated in clusters, whose size ‰ FAT12: FAT file system using 12-bit cluster addressing are determined by the size of the volume. ‰ FAT16: FAT file system using 16-bit cluster addressing „ Updating the FAT table is very important as well as time ‰ FAT32: FAT file system using 32-bit cluster addressing; Win95 consuming. SR2 and later ‰ If not regularly updated, it can lead to data loss ‰ FAT or FATxx: File systems that use File Allocation Tables „ FAT supports only read-only, hidden, system, and archive file attributes. FAT Structure „ The File Allocation Table

‰ A series of addresses that is accessed as a lookup table to „ The FATxx volume is divided into four areas: see which cluster comes next, when loading a file or ‰ The boot record traversing a directory. ‰ The File Allocation Tables ‰ FAT is a vital data structure ⇒ two copies (FAT1 & FAT2) ‰ The root directory so that corruption of the FAT can be detected and repaired ‰ The data area „ The root directory „ The boot record ‰ Fixed in length and always located at the start of the ‰ The first sector of a FAT12 or FAT16 volume volume (after the FAT) in FAT12 and FAT16 volumes

‰ The first 3 sectors of a FAT32 volume. „ FAT32 treats the root directory as just another cluster chain ‰ If the volume is bootable, then the first sector of the boot in the data area record also contains the code required to enter the file „ The data area ⇒ data is stored system and boot the OS. ‰ Fill the rest of the volume, and is divided into clusters

Advantages of FAT Disadvantages of FAT

„ It is not possible to perform an undelete under „ When using drives or partitions of over 200 MB the Windows NT on any of the supported file systems. FAT file system should not be used. ‰ As the size of the volume increases, performance with ‰ Undelete utilities try to directly access the hardware, which cannot be done under Windows NT FAT will quickly decrease „ It is not possible to set permissions on files that are „ However, if the file was located on a FAT partition, FAT partitions. and the system is restarted under MS-DOS, the file „ FAT partitions are limited in size to a maximum of can be undeleted. ‰ 4 Gigabytes (GB) under Windows NT „ The FAT file system is best for drives and/or partitions ‰ 2 GB in MS-DOS under approximately 200 MB, because FAT starts out with very little overhead. New Technology File System (NTFS) Goals of NTFS

„ NTFS continues to organize files into directories. „ Reliability

„ Unlike FAT ‰ NTFS is a recoverable file system because it keeps track of transactions against the file system ‰ No "special" objects on the disk ‰ Desirable for high end systems and file servers ‰ No dependence on the underlying hardware, such as 512 byte sectors. „ Added functionality

‰ No special locations on the disk, e.g., FAT tables ‰ NTFS provides a rich and flexible platform for other file systems to be able to use

‰ NTFS fully supports the Windows NT security model and multiple data streams „ Support POSIX requirements „ Removal of the limitations of the FAT file systems

„ Support POSIX requirements „ Removing Limitations

‰ Case Sensitive Naming: ‰ NTFS has greatly increased the size of files and volumes, so that they can now be up to 2^64 bytes. „ Under POSIX, README.TXT, Readme.txt, and readme.txt are all different files ‰ All NTFS filenames are Unicode based, and 8.3 filenames are kept along with long filenames. ‰ Additional Time Stamp: „ Supply the time at which the file was last accessed

‰ Hard Links

„ When two different filenames, which can be located in different directories, point to the same data Advantages of NTFS Disadvantages of NTFS

„ NTFS is best for use on volumes of about 400 MB or „ Do not use NTFS on a volume that is smaller than more. approximately 400 MB ‰ The amount of space overhead involved in NTFS, typically ‰ Performance does not degrade under NTFS, as it does use at least 4 MB of drive space on a 100 MB partition under FAT, with larger volume sizes. „ No file encryption built into NTFS „ The recoverability designed into NTFS is such that a ‰ Someone can boot under MS-DOS, or any OS, and use a low-level disk editing utility to view data stored on an NTFS user should never have to run any sort of disk repair volume utility on an NTFS partition. „ It is not possible to format a floppy disk with the NTFS file system.

‰ Windows NT formats all floppy disks with the FAT file system because the overhead involved in NTFS will not fit onto a floppy disk.