2026-03-08

RAID Array & Server Glossary of Computer Terms (Letter H)

DATARECOVERYUNION.COM03 mins

Host
Any computer system to which disks are attached and accessible for data storage and I/O.

Host adapter
A bus-based (PCI, EISA, ISA) hardware device, such as an add-in card or ASIC, that converts the timing and protocol of a host’s memory bus and an I/O bus.

Hot spare
RAID storage feature that allows a spare drive (or other component) to be configured for automatic (in contrast to hot-swap) replacement and reconstruction in the event of a disk failure. Users can remain on-line and continue to access data.

Hot Replacement of Disks
The design of all Mylex controllers allows for the replacement of failed hard disk drives without interruption of system service. In the event of a SCSI drive failure on a properly configured system (where the data redundancy features of the controller are used), the system generates a message to alert the system operator.

When a replacement drive becomes available, the system operator can remove the failed disk drive, install a new disk drive, and instruct the controller to “rebuild” the data on the new drive, all without interrupting system operations. Once the rebuild is complete, the controller will be brought back into a fault tolerant state. See also Hot Swap.Hot SpareA physical disk drive not part of a system drive that the controller can use to automatically rebuild a critical system drive. The hot spare drive must have at least as much capacity as the largest disk drive in the array or the rebuild may not start. See also Hot Standby and Standby Replacement of Disks.

Hot Standby
A redundant component in a fault tolerant storage system that has power applied and is ready to operate, but which does not perform its task as long as the primary component for which it is standing by is functioning properly. See also Hot Replacement of Disks and Hot Spare.

Read More

Linux File Structure

DATARECOVERYUNION.COM05 mins

linux file structureLinux file structure files are grouped according to purpose. Ex: commands, data files, documentation. Parts of a Unix directory tree are listed below. All directories are grouped under the root entry “/”.

root – The home directory for the root user
home – Contains the user’s home directories along with directories for services

  • ftp
  • HTTP
  • samba
  • george

bin – Commands needed during bootup that might be needed by normal users
sbin – Like bin but commands are not intended for normal users. Commands run by LINUX.
proc – This filesystem is not on a disk. It is a virtual filesystem that exists in the kernels imagination which is memory.

  • 1 – A directory with info about process number 1. Each process has a directory below proc.

usr – Contains all commands, libraries, man pages, games and static files for normal operation.

  • bin – Almost all user commands. some commands are in /bin or /usr/local/bin.
  • sbin – System admin commands not needed on the root filesystem. e.g., most server programs.
  • include – Header files for the C programming language. Should be below /user/lib for consistency.
  • lib – Unchanging data files for programs and subsystems
  • local – The place for locally installed software and other files.
  • man – Manual pages
  • info – Info documents
  • doc – Documentation
  • tmp
  • X11R6 – The X windows system files. There is a directory similar to usr below this directory.
  • X386 – Like X11R6 but for X11 release 5

boot – Files used by the bootstrap loader, LILO. Kernel images are often kept here.
lib – Shared libraries needed by the programs on the root filesystem

  • modules – Loadable kernel modules, especially those needed to boot the system after disasters.

dev – Device files
etc – Configuration files specific to the machine.

  • skel – When a home directory is created it is initialized with files from this directory
  • sysconfig – Files that configure the linux system for devices.

var – Contains files that change for mail, news, printers log files, man pages, temp files
file

  • lib – Files that change while the system is running normally
  • local – Variable data for programs installed in /usr/local.
  • lock – Lock files. Used by a program to indicate it is using a particular device or file
  • log – Log files from programs such as login and syslog which logs all logins and logouts.
  • run – Files that contain information about the system that is valid until the system is next booted
  • spool – Directories for mail, printer spools, news and other spooled work.
  • tmp – Temporary files that are large or need to exist for longer than they should in /tmp.
  • catman – A cache for man pages that are formatted on demand

mnt – Mount points for temporary mounts by the system administrator.
tmp – Temporary files. Programs running after bootup should use /var/tmp.

Read More

How does HDD store data?

DATARECOVERYUNION.COM02 mins

How does HDD store data?Hard disk drives store data on one or more metal oxide platters. These platters spin at a rate of 3600-10,000 revolutions/minute, hold magnetic charges. A read-write head attached to an actuator arm actually floats on a cushion of air, 1-2 micro-inches (one millionth of an inch) above the surface of the platters. Data flows to and from these heads via electrical connections. Any force alters this process may cause data loss.

Ten years ago hard drives stored 40 Megabytes (MB) of data. Today’s hard drives store data up to 2000 gigabytes (GB) on a smaller surface. Increasing storage capacities amplify the impact of data loss. As more and more data is stored in smaller and denser areas, mechanical precision becomes crucial.

As a part of this advancing technology, the drive tolerance (distance between the read/write head and the platter where data is stored) is steadily decreasing. A slight nudge, an unstable power surge or a dust introduced into the drive may cause the head to touch the platter, resulting in a head crash, PCB burnt, bad sectors, etc. In some situations, the data residing in the area touched by the head may be permanently destroyed.

The current tolerance drives is 1-2 micro-inches (millionths of an inch). Comparatively, a speck of dust is 4-8 micro-inches and human hair 10 micro-inches. These sizes contaminants can cause serious data damage.

Read More

SATA/EIDE Hard Drive is detected as a SCSI Device?

DATARECOVERYUNION.COM04 mins

SATA/EIDE Hard Drive is detected as a SCSI Device?1. Why is my Serial ATA hard drive detected as a SCSI device in Windows?
A Serial ATA hard drive is detected as a SCSI device in Windows Device Manager.

This issue could have several causes:

  • The Serial ATA controller (on the motherboard or through a PCI controller card) is assigned default Windows drivers. If Windows is unable to determine exactly what type of device the Serial ATA controller is, it will attempt to assign the closest matching device drivers. Since Serial ATA works using the same principles as SCSI, Windows will assign a Serial ATA controller a SCSI designation.
  • The Serial ATA controller’s (on the motherboard or through a PCI controller card) bus architecture is taken from a SCSI HBA (Host Bus Adaptor). Many companies that produce Serial ATA controllers also produce SCSI controllers. These companies often use an altered version of a SCSI HBA on Serial ATA controllers.
  • The Serial ATA hard drive is connected to a Serial ATA RAID controller. RAID and SCSI controllers have the same device designation in Windows therefore a Serial ATA hard drive will be detected as a SCSI device.

Since this issue is “by design” of the Windows operating system, there is no resolution implied or necessary. Any Serial ATA hard drive designated as a SCSI device will work properly at full performance and capacity. There may be device drivers for the Serial ATA controller that will list the hard drive as a Serial ATA device. Please contact your computer, motherboard, or Serial ATA controller manufacturer for any driver or BIOS updates.

2. Why is my EIDE drive displayed as a SCSI drive in Device Manager in Windows 2000/XP?
An EIDE drive is displayed as a SCSI drive in Windows 2000/XP.

It is common for Windows 2000 and XP to list EIDE drives as SCSI devices in Device Manager when they are connected to non-standard IDE controllers such as a Promise or SIIG controller card. This also occurs when the drive is connected to a specialized ATA or RAID port that is integrated into the motherboard. As long as you have the proper drivers loaded for the controller and are not experiencing any issues while using the drive, there is no cause for concern.

Read More