Notes on Windows NT Disk Storage

Drive — a physical unit of storage. Most computers have at least one hard drive.

Partition — a subdivision of a drive. A drive may have one or more partitions.

Volume — a logical file system.

Drive Letters — Drive letters (such as C: or E:) are assigned to volumes.

File System Comparison

FAT

NTFS

low overhead

File level local security

long file names

long file names

4 GB max partition size

2 TB or 16 EB max partition size

common to many OS

supports compression

required for RISC system partition

transaction based recoverabiltity

max of 512 entries in root

support for cluster remapping

support for Macintosh files

POSIX support

supports volume sets

NT cannot read FAT32 (available on Windows 98 and some OEM versions of Windows95).

Removable media is usually formatted as FAT. It can be formatted as NTFS, but the computer must be shut down and restarted to change disks.

You can convert from FAT to NTFS using the convert program,

convert drive: /fs:ntfs

There is no provision for converting from NTFS to FAT.

Partitions

There can be up to 4 primary partitions on a disk.

Extended partitions may contain logical drives.

The active partition is the one that is booted.

The system partition contains the boot data.

The boot partition contains the operating system.

 

Storage Organizations

Standard volumes A regular formatted partition. The file system uses one partition on one disk. This is the only format supported by Windows NT Workstation, Windows 95 or DOS.

Volume Sets Up to 32 partitions on multiple drives can be combined into a single volume set. A volume set has a single drive letter. Data is stored on one partition until it is full and then additional data is stored on the next partition. Failure of a single drive in a volume set will result in the loss of the complete volume set.

Stripe Sets Data is written in a round robin fashion across multiple drives in 64K blocks. Requires two or more partitions on separate physical drives. Improves performance by allowing multiple drives to serve a single I/O request.

Stripe Sets with Parity Similar to regular stripe sets, but the XOR of each block is written to an additional drive. If any of the drives in a stripe set with partity fails, the data will still be available. Requires three or more partitions on separate physical drives. X disks with Y MB on each will provide a file system with (X-1)*Y available space.

Mirroring Data written to a disk is copied to another identical disk. If one of the disks in a mirror set fails, the data can still be recovered from the other disk. This is software RAID 1. Two drives with Y MB on each will provide a file system with Y MB.

Duplexing This is the same as mirroring expect that the two mirror partitions must be on separate controllers. Provides additional fault tolerance.

Hardware RAID RAID is Redudant Array of {Inexpensive, Independent} Disks. A RAID controller makes multiple disks appears as one large file system.

RAID 0 Stripe set organization for improved performance.

RAID 1 Mirrored disks for fault recovery.

RAID 5 Stripe set with Parity organization for performance and fault tolerance.

Server replication Data is stored on two separate server computers. When a file is closed, it is copied to the other server.

Comparison of File Organizations

number of disks

fault tolerance

performance

volume

1

none

5

A single partition on a disk.

volume sets

1 or more

worst

5

A combination of multiple partitions to form one large file system.

striping

2 or more

worst

8

Data is written simultaneously across multiple disks in 64K blocks.

striping with parity

3 or more

1 disk can fail

7

Striping with an extra disk for fault tolerance.

mirroring

2

1 disk can fail

4

All data is written to two identical disk partitions.

duplexing

2

1 disk or control can fail

5

Mirroring with separate disk controllers.

hardware RAID 0

[2 or more]

worst

10

striping

hardware RAID 1

[2]

1 disk can fail

5

mirroring

hardware RAID 5

[3 or more]

1 disk can fail

9

striping with parity

server replication

2 or more

best

4

Data is copied to a second server when the file is closed and not used for 2 minutes. Only closed files are copied to second server.

 

Compression

Directories or individual files can be compressed.

You can compress files from Windows NT Explorer or compact.exe

Compressed file show in blue if the Windows Explorer option is selected.

Backup

Backups are extremely important. All disks will fail sometime.

Backups should rotate through a series of tapes

Backups can be full or incremental.

Off site backups are necessary.

ARC Pathnames

Advanced RISC Computing (ARC) naming is used to identify drive hardware.

for Intel X86 computers:

multi(W)disk(X)rdisk(Y)partition(Z)

where:

W is the ordinal number of the controller (usually 0)

X is not used (always 0)

Y is the ordinal for the disk on the controller. (0 or 1 for disks connected to the primary controller and 0 through 3 for disks on a dual channel EIDE controller.)

Z is the partition number. Numbered starting at 1.

for RISC and Intel X86 computers:

scsi(W)disk(X)rdisk(Y)partition(Z)

where:

W is the ordinal number of the controller.

X is the SCSI ID of the disk.

Y is the SCSI logical unit number (LUN) of the disk. (Almost always 0)

Z is the partition number. Numbered starting at 1.

last updated on 01/02/04