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

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

2. 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

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

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. 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”

11. Entering the Partition Size

12. 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

13. 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.

14. Formatting • Assigning a drive letter

15. 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

16. 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

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

18. 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

19. 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

20. 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

21. Disk Striping • Advantages • 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

22. 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 Parity block Row 1 Parity block Row 2 Parity block Row 3

23. 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.

24. 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

25. 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

26. 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)

27. 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)

28. 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

29. 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

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

31. 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

32. 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

33. 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

34. Configuring Server RAM Hints

35. 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

36. 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

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

38. 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