Chapter 12.3 Mass-Storage SystemsChapter 12-3 Mass-Storage SystemsDisk ManagementSlide 4Disk Management – Preliminary CommentsDisk Management – Disk FormattingDisk Management – Disk SectorsSlide 8Disk Management – Low-Level FormattingSlide 10Slide 11Disk Management – Low-Level Formatting- Raw DiskDisk Management – That Boot BlockWindows 200 Boot ApproachBooting from a Disk in Windows 2000Bad Blocks – IDE ControllersBad Blocks – SCSI ControllersBad Blocks – SCSI Controllers – moreSwap Space ManagementSwap-Space ManagementSwap Space Management - IntroductionSwap Space UseSwap Space LocationRAIDRedundant Arrays of Independent Disks (RAID)Redundant Arrays of Inexpensive Disks (RAID)Improvement in Performance via ParallelismEnd of Chapter 12.3Chapter 12.3 Mass-Storage SystemsChapter 12.3 Mass-Storage Systems.2/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsChapter 12-3 Mass-Storage SystemsChapter 12-3 Mass-Storage SystemsChapter 12-1:Overview of Mass Storage StructureChapter 12-2:Disk AttachmentDisk SchedulingChapter 12-3: Disk Management Swap-Space Management RAID StructureChapter 12-4Stable-Storage ImplementationTertiary Storage DevicesOperating System IssuesPerformance Issues.3/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk ManagementDisk Management.4/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk ManagementDisk ManagementWe will discuss three very important topics:Disk FormattingBoot Blocks, and Bad Blocks.5/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Preliminary CommentsBefore a disk is first put into use, it must be formatted.But the disk can (and does, typically) support a variety of often diverse uses – fromOperating system needs andUser needs, and Certain specialized needs for sometimes special applications.So, the disk must / can be formatted in a number of ways – and is.Further, when disks are manufactured and sent out for use, they often have bad spots (bad sectors).This is the normThus any kind of formatting must account for bad spots on the disk and map logical blocks into physical sectors.So, there’s a lot of important information in this section..6/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Disk FormattingInitially a disk is divided into sectors that the disk controller can read from and write to.Recall: the disk controller is itself a small, very specialized processor and executes a restricted instruction set. The instruction set deals primarily with instructions dealing with I/O and instructions dealing with device operations themselves.Instructions include requests such as: input and output (open, close, read, write, etc. and additional instructions needed to control and manage the disk operations (is device ready; timing; much more)As stated in previous lectures, instructions to the disk controller and other low level privileged instructions take the form of ‘commands’ and ‘instructions’ (depends on the computing system)Commands handled interpretively; Instructions – generally assembler level – are a bit different..7/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Disk SectorsFormatting the disk into sectors is referred to as low-level formatting.Typical sector size is 512 bytes; others are available, such as 256 bytes, 1024 bytes (IK) and others. 512 is the norm.Each sector itself contains a specific data structure consisting of a header, body of the sector, and a trailer.Headers and Trailers are used for control information needed by the disk controller. These typically include:Sector number (can check against the request for I/O) - Usually found in header.Error Correction Codes (ECC) - Usually found in trailerData area itself – generally 512 bytes..8/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Disk SectorsThe error correcting code (not exactly the same as those used in main memory – but the thinking and specific bits are very similar…) is generated when data is written to the data portion.There are a variety of formulas used in generating ECCs.When a read takes place, the hardware calculates the code based on the number and position of specific bitsand compares it to the code stored in the sector.If different, the sector is somehow corruptedBecause the ECC is error-correcting, the bit (hopefully one) may be both identified (detected) and corrected.This is called a soft error and this phenomenon is passed on to system administrators and tech reps for maintenance concerns.We talk a lot about ECC, parity, redundancy and more when we discuss RAID ahead...9/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Low-Level FormattingUsually the disk is low-level formatted as part of production.Part of this formatting includes a process to designate a number of bytes of the data portion of a sector. Header and trailer sizes are generally fixed because they are hardware processed.As stated, the disk may be ‘divided’ into specific portions of the disk (called partitions) which may be used for specific needs. Because of the physical characteristics of disk access, partitions are normally allocated ‘in cylinders.’Each partition is essentially a separate logical disk.Three typical partitions arePartition for the operating system’s executable codePartitions for user filesOften, partition(s) of raw disk..10/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDisk Management – Low-Level FormattingGiven that three (or more) partitions are established, these partitions need to be made ready.After partitioning, step 2 is logical formatting (creation of a file system).Here, the OS needs to establish several data structures for control and management.These partitions are initialized and include structures such as empty directories and other structures (like memory maps) to be used to manage free and allocated regions necessary during normal operations. In truth, there is much more than just these….11/38Silberschatz, Galvin and Gagne ©2005Operating System ConceptsReally – much more is done depending on the OSAre we using virtual memory?