Windows NT Filesystems
SCSI disk drives each contain their own controller, while IDE drives rely on a controller card or controller on the motherboard. RISC computers require a 2M FAT partition for a system partition.
A maximum of four primary partitions are allowed with one extended partition. An extended partition may contain several logical partitions. Drive letter assignment begins at the first hard drive, primary partitions are numbered first, then logical drives. Drive letter assignment then continues with the next physical drive. NT allows the drive letters to have custom settings by using the Disk Administrator program. Only one partition may be active at a time. The computer will use the boot sector of the active partition to begin the boot process. Terms:
- Sector Translation - Used by SCSI disks to support more than 1024 cylinders.
- LBA - Large block allocation is used by IDE disks to support more than 1024 cylinders.
- Volume - Disk table of contents allowing file indexing. There can be up to 32 partitions per volume set.
The NTFS filesystem uses BTREE allocation which means data is stored on the drive in 8 Meg bands separated by 2K of allocation between each band.
- Minimum NTFS partition size is 50Mb. 25% of drive space is used for directory information.
- Deleting files in the recycle bin permanently removes them.
- NT only compresses files that benefit from compression even if the compression bit is set.
- NT compression favors speed rather than size.
- NTFS supports POSIX which uses filename case sensitivity, hard links, and stores last access time information. Names for POSIX can't include ? " / \ < > * | :.
- Shortcuts have a .LNK extension that is never visible to windows explorer.
- NTFS uses a B-tree directory structure.
- NTFS filesystems can't be converted to HPFS or FAT.
- ACLCONV.EXE utility retains the security attributes of an HPFS volume used by OS/2 or a LAN Manager Server.
- Uses a linked list filesystem to determine drive space use.
- VFAT - This is an extension to the original FAT filesystem that supports long filenames. MS-DOS version 7, Windows 95, and NT4.0 can use this filesytem.
- FAT32 - Supports large volumes and cluster sub-allocation. Windows 95 OEM Release 2 and Windows 98 uses this filesystem.
Fault Tolerance Mechanisms
NT workstation supports stripe sets but not mirroring or any other fault tolerance exclusive of sector sparing.
- Disk mirroring - One disk is a mirror copy of the other. This is geared for reliablilty, not speed. The boot and system partition may be mirrored. Mirrored volumes must be of the same size. Mirroring is done by clicking on the volume to be mirrored while holding the CTRL key down, then clicking on some free space of equal or greater size while the CTRL key is held down. Then click "Fault Tolerance", "mirror", and "establish mirror". To break a mirror, click on the mirror, and break.
- Disk Striping - Data is split into sections with part of the data being written to each disk in parallel. Can use 2 to 32 disks. This provides speed but not reliability unless disk striping with parity is used. Each partition in a stripe set must be the same size. The boot or system partition may not be part of a stripe set. Data is stored in 64K blocks. Must drives be of the same type to be part of a stripe set? (I don't think so.)
- Disk striping with parity - The same as disk striping except an additional disk that stores parity information is used. Can use 3 to 32 disks. The parity information may be used to recreate the contents of a failed drive. At least three disks are required to create a stripe set with parity. To make a stripe set from Disk Administrator, click on three areas of free space on three drives. From the fault tolerance menu choose "create stripe set with parity". Select the "Partition" menu, "commit changes". Reboot, then format the stripe set by highlighting the stripe set and selecting "tools", and "format".
- Disk duplexing - Each disk gets its own controller so one controller failure can't bring both disks down. Without redundant controllers, this is the same as disk mirroring.
- Replication - One server is a complete copy of another in case one server fails. One is used as a primary server and the other is a backup server.
Redundant Array of Inexpensive disks (RAID)
RAID is a fault tolerant method of storing data, meaning that a failure can occur and the system will still function. When RAID is hardware supported, the RAID hardware will perform parity calculations, thus freeing the system. The various RAID categories are:
- 0 - Disk striping - Data is written across multiple drives in parallel. Different parts of the data is written at the same time to more than one drive. If there are two drives, half the data is written to one drive, while the rest of the data is written to the other drive. All partitions on striped drives must be the same size. No fault tolerance is provided with RAID-0.
- 1 - Disk mirroring - All the data is written to two drives so each drive has a complete of all stored data. If one drive fails, the other can be used to get a copy of the data. To be more fault tolerant, more than one controller card may be used to control the mirrored hard drives. This is called disk duplexing and will allow the system to keep functioning if one controller card fails.
- 2 - Disk striping with error correction codes (ECC).
- 3 - Disk striping with ECC parity information stored on a separate drive.
- 4 - Disk striping with blocks with parity information stored on a separate drive.
- 5 - Disk striping with blocks with parity information stored using multiple drives. Uses five disks with one fifth of each one to store parity information.
NT Server supports RAID 0, 1, and 5.
Volume sets are used to extend volumes across multiple hard drives. Neither the system nor boot partition may be part of a volume set. A volume set may use different type drives (IDE, SCSI) and can be any combination of FAT, NTFS or filesystem that NT can use.
The boot partition cannot be extended in size.
Repairing a mirrored drive
- Replace the failed hard drive.
- Break mirror set using the "Disk Administrator" fault tolerance menu.
- Create a new mirror set.
Tape Drive Addition
Tape drives are added using the "Tape Devices" applet in the Control Panel. You can allow the tape to be detected automatically or use the drivers tab to select and add a driver.