.NET Notes

.NET Windows Admin (2k, XP, 2003, Commerce Server)

Version 0.0 14/9/2003 by Samar

  1. DOS
  2. MS Office
  3. Viruses;

1. DOS

2. MS Office

MS Word

Outlook

2. Viruses

    3 Types of Viruses
  1. File Infector: attach to prog files (usu. .com or .exe, maybe .sys, .ovl, .prg, .mnu); email attachmts
  2. Boot Sector/System/Boot-record Infector: infect dos boot sector on FD + MBR on HD, eg if bootg from infected FD
  3. Macro Virus: most common viruses, least damage, infact ms Word, usu. insert unwanted words
  4. messages: Run > net send dsil-012 hello from samar

RAID

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly also increases fault-tolerance.

A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

In a single-user system where large records, such as medical or other scientific images, are stored, the stripes are typically set up to be small (perhaps 512 bytes) so that a single record spans all disks and can be accessed quickly by reading all disks at the same time.

In a multi-user system, better performance requires establishing a stripe wide enough to hold the typical or maximum size record. This allows overlapped disk I/O across drives. There are at least nine types of RAID plus a non-redundant array (RAID-0): 


 * RAID-0. This technique has striping but no redundancy of data. It
   offers the best performance but no fault-tolerance.
 * RAID-1. This type is also known as disk mirroring and consists of 
   at least two drives that duplicate the storage of data. There is no
   striping. Read performance is improved since either disk can be read
   at the same time. Write performance is the same as for single disk
   storage. RAID-1 provides the best performance and the best
   fault-tolerance in a multi-user system.
 * RAID-2. This type uses striping across disks with some disks storing
   error checking and correcting (ECC) information. It has no advantage
   over RAID-3.
 * RAID-3. This type uses striping and dedicates one drive to storing
   parity information. The embedded error checking (ECC) information is
   used to detect errors. Data recovery is accomplished by calculating
   the exclusive OR (XOR) of the information recorded on the other
   drives. Since an I/O operation addresses all drives at the same
   time, RAID-3 cannot overlap I/O. For this reason, RAID-3 is best for
   single-user systems with long record applications.
 * RAID-4. This type uses large stripes, which means you can read
   records from any single drive. This allows you to take advantage of
   overlapped I/O for read operations. Since all write operations have
   to update the parity drive, no I/O overlapping is possible. RAID-4
   offers no advantage over RAID-5.
 * RAID-5. This type includes a rotating parity array, thus addressing
   the write limitation in RAID-4. Thus, all read and write operations
   can be overlapped. RAID-5 stores parity information but not
    redundant data (but parity information can be used to reconstruct
    data). RAID-5 requires at least three and usually five disks for the
    array. It's best for multi-user systems in which performance is not
    critical or which do few write operations.
  * RAID-6. This type is similar to RAID-5 but includes a second parity
    scheme that is distributed across different drives and thus offers
    extremely high fault- and drive-failure tolerance. There are few or
    no commercial examples currently.
  * RAID-7. This type includes a real-time embedded operating system as
    a controller, caching via a high-speed bus, and other
    characteristics of a stand-alone computer. One vendor offers this
    system.
  * RAID-10. This type offers an array of stripes in which each stripe
    is a RAID-1 array of drives. This offers higher performance than
    RAID-1 but at much higher cost.
  * RAID-53. This type offers an array of stripes in which each stripe
    is a RAID-3 array of disks. This offers higher performance than
    RAID-3 but at much higher cost.

3. Security

References