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

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Chapter 6 Configuring Server Storage, Backup,
and Performance Options
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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

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Learning Objectives

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

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Hard Disk Basics

• Low-level format
• 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

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Hard Disk Basics

• Sectors
• 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

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A Disk Divided into Tracks and Sectors
Tracks
Sectors within a track
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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

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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

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Disk Partitions

• Boot loader
• 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

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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

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Entering the Partition Size
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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

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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 its made up
  of.

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Formatting

• Assigning a drive letter

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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

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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

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Implementing Disk Redundancy

• Operating system disk protection
• Disk striping
• Striping with parity
• Disk mirroring

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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

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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

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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
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Disk Striping

• Advantages
• speeds access to data
• rotational and seek latencies
• spreads out wear tear
• Disadvantages
• if one disk fails, cant re-create data
• different options (RAID levels) address this
• Tradeoffs
• one adapter for all disks, or one each

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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
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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.

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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

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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

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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)

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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)

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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

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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

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Configuring a Server to Improve Performance

• Configuring virtual memory
• Configuring memory to match the user load

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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

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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

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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

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Configuring Server RAM Hints
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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

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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

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Chapter Summary

• Disk performance affected by
• Fragmentation
• Distribution of files across multiple disks
• RAM configuration
• Virtual memory

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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

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