Chapter 6: Configuring Server Storage, Backup, and Performance Options

Learning Objectives Partition and format hard disks Explain types of disk partitions Create volume sets Extend a disk volume Implement disk redundancy through striped sets, striped sets with parity, and mirrored sets continued

Learning Objectives Perform disk backups Develop a tape rotation scheme Configure server memory to improve performance Configure Windows NT Server for a UPS

Hard Disk Basics Low-level format Tracks A software process that marks tracks and sectors on a disk Necessary before a disk can be partitioned and formatted Tracks Concentric rings that cover an entire disk Each ring is divided into sectors in which data are stored

Hard Disk Basics Sectors Other nomenclature A portion of a disk track Disk tracks are divided into equal segments, or sectors Other nomenclature tracks also known as “cylinders” “heads” are number of r/w devices LBA = logical block address

A Disk Divided into Tracks and Sectors Sectors within a track

Disk Partitions Partitioning: The process of marking a group of tracks and sectors in preparation for a file system breaks a physical disk into logical volumes Free space: Disk space not yet partitioned for use by a file or operating system different from “free space” (i.e. space available to store files) within a volume

Disk Partitions Master boot record (MBR): Data stored in the first sector of a disk, including startup information and information about disk partitions Partition table Table containing information about each partition on a disk Provides information to the computer about how to access the disk

Disk Partitions Boot loader Various choices mini-program, lives in MBR or first sector of partition presents menu of boot choices to user generally has timeout and default choice Various choices NT boot loader OS/2 boot manager Linux “LILO” generally, independent of the OS

Primary and Extended Partitions Primary partition: Partition or portion of a hard disk that is bootable Extended partition: Partition that is created from (otherwise) unpartitioned disk space; contains “logical partitions”

Entering the Partition Size

Partition Types Active partition: Partition from which a computer boots, or starts can change active partition to enable booting of other OSs Boot partition: Partition that holds the Windows NT\Winnt folder containing the system files boot partition gets special treatment by OS

Formatting Formatting: A process that prepares a hard disk partition for a specific file system Volume: loosely defined as “an amount of storage”. Can be a partition (any sort), a stripe set, etc. Generally seen by users as a drive letter (ex. D:) no matter what it’s made up of.

Formatting Assigning a drive letter

Creating Volume Sets Volume set: Two or more formatted partitions (volumes) that are combined to look like one volume with a single drive letter Advantage Ability to manage several small disk drives more easily or to maximize the use of scattered pockets of disk space across several disks Disadvantage If one disk in the volume set fails, the entire volume is inaccessible

Extending a Volume Add (e.g.) another disk until larger disk drives are purchased increases available space to users Same risks as volume set disk failure

Implementing Disk Redundancy Operating system disk protection Disk striping Striping with parity Disk mirroring

Operating System Disk Protection Hot fix: A data recovery method that automatically stores data elsewhere when a damaged area of disk prevents that data from being written “Hot” because it happens without interruption to the system

Operating System Disk Protection Sector sparing: A fault-tolerance method that reserves certain hard disk sectors so that they can be used when a bad sector is discovered Cluster remapping: A fault-tolerance technique that flags a damaged cluster and finds an undamaged cluster on which to write data “cluster” is mostly analogous to a sector

Disk Striping Stripe set: Two or more disks set up so that files are spread in blocks across the disks Disk 1 Disk 2 Disk 3 Disk 4 Disk 5 Row 1 Row 2 Row 3

Disk Striping Advantages Disadvantages Tradeoffs speeds access to data rotational and seek latencies spreads out wear & tear Disadvantages if one disk fails, can’t re-create data different options (RAID levels) address this Tradeoffs one adapter for all disks, or one each

Striping with Parity Stripe set with parity: Three or more disks in which files are spread across the disks in blocks, and a parity block is written on each disk to enable data recovery should one disk in the set fail Disk 1 Disk 2 Disk 3 Disk 4 Disk 5 Row 1 Parity block Parity block Row 2 Parity block Row 3

Striping with Parity Definition of “parity” the result of a mathematical function performed on the data, which can be used to reconstruct what the original data were There must be 3 or more disks to do this Recall server hardware discussion hot-swap disks versus power-down, etc.

Disk Mirroring Involves creating a “shadow” copy of data on a backup disk also “duplexing” - different adapters Advantages Most guaranteed form of disk fault tolerance Well suited for mission-critical data Disadvantages Doubles time needed to create or update information

Increasing Disk Performance and Longevity Make sure that one disk is not working harder (e.g. accessed more often) than other disks in a multiple-disk server Use striping or striping with parity Relocate files to distribute disk access more evenly Use defragmenting to reorganize files to reduce the number of empty spaces between files

Disk Security Through Backup Techniques Advantages of local (eg. one per server) tape drive backups Causes no extra load on network Can perform backups on a multiple server network even if one tape drive fails Provides more assurance that the Registry is backed up Can also back up on other media Jaz disks, ZIP disks, writable CD-ROMs, etc. another hard drive (disaster recovery)

Disk Security Through Backup Techniques Full backup: Backs up all volumes, directories, and files Incremental backup: Backs up only those files that have changed since the previous backup generally, much smaller than full backup quicker to perform less media needed (number of tapes)

Backup Options Normal: Same as full file-by-file backup Copy: Only files or directories selected Incremental: Only files with archive attribute Differential: Same as incremental but does not remove archive attribute Daily: Only files that have been changed/updated on the day of backup

Tape Rotation Helps ensure alternatives in case there is a bad or worn tape e.g., Tower of Hanoi procedure: Rotates tapes so that some are used more frequently than others depends on importance of data, budget for tapes, skill and time of backup operator Consider off-site storage for disaster recovery

Configuring a Server to Improve Performance Configuring virtual memory Configuring memory to match the user load

Configuring Virtual Memory Virtual memory: Disk space allocated to temporarily hold data when there is not enough free RAM much slower than RAM (e.g. not a replacement) Paging: Moving blocks of information from RAM to virtual memory on disk Page file: Disk space reserved for use when memory requirements exceed available RAM General rule for sizing = Amount of installed RAM + 12 MB

Configuring Virtual Memory System “swaps out” pages to disk as needed ex. when multitasking, use RAM for current program, put others on disk temporarily happens automatically; neither user nor programmer has to do anything Can dramatically affect performance sometimes greatly increases contention for the disk containing the pagefile if misused, system spends all its time copying data and very little doing actual useful work adding RAM memory (e.g., avoiding VM) is better

Configuring Memory to Match the User Load Server functions Use RAM and paging Software applications Printing Currently running services Network connectivity functions Use RAM only Number of user connections

Configuring Server RAM Hints

UPS Fault Tolerance Uninterruptible power supply (UPS): A device that provides immediate battery power to equipment during a power failure or brownout for a limited time period Online UPS: Battery backup device that provides power to equipment directly from its batteries at all times Offline UPS: Battery backup device that waits until there is a power decrease or sag before switching to battery power

Chapter Summary Properly setting up disk storage is as important as selecting it. Partition disk drives through the Disk Administrator After partitions are set up and formatted, implement a fault-tolerance method. Disk striping Striping with parity Disk mirroring continued

Chapter Summary Disk performance affected by Fragmentation Distribution of files across multiple disks RAM configuration Virtual memory continued

Chapter Summary Establish a tape backup method to guard against data loss. Full and partial backup techniques Tape rotation Also, can protect against power outages with a UPS