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Chapter 9: Glossary
Network Storage System (NSS) Administrator Guide
Chapter
9
DHCP:
Dynamic Host Configuration Protocol. Software that dynamically assigns IP addresses to
devices on a TCP/IP network. DHCP software typically runs in servers and is also found in network
devices such as ISDN routers and modem routers that allow multiple users access to the Internet.
Newer DHCP servers dynamically update the DNS servers after making assignments.
DiffServ (Differentiated Services):
A scalable IP Layer 3 method for classifying, managing network
traffic, and providing QoS (Quality of Service) guarantees on an IP network. DiffServ is often used
to provide low-latency, guaranteed service to time-sensitive network traffic like voice or video while
concurrently providing best-effort traffic guarantees to non-time sensitive Web traffic (such as email)
or file transfers.
Disk Quotas:
In a NAS, a limit set by a network administrator that restricts certain aspects of
filesystem usage. There are four types of disk quotas: 1) Usage (or block) quota sets a limit on the
amount of storage space (measured in MB or GB) that connected users or groups can use, 2) File (or
inode) quota sets a limit for a specific number of directories or files that connected users or groups
can use, 3) Usage or File quotas are considered Hard quotas, 4) Soft quota is a way, set by the
administrator, to define a warning level that alerts users that they are nearing their specified hard
quota limit.
Disk Tax/Disk Overhead:
The limitation of hard disk drive (HDD) capacity when specific RAID
configurations that use mirroring or redundancy are applied to an array.
DNS:
Domain Name System (or Service or Server). An Internet service that translates domain names
into IP addresses. While domain names are alphabetic and easier to remember, the Internet uses IP
addresses. When you use a domain name, a DNS service must translate the name into the
corresponding IP address. The DNS system is its own network. If one DNS server does not know how
to translate a particular domain name, it asks another one, and so on, until the correct IP address is
returned.
Domain:
The name that identifies a computer connected to the Internet. For example,
www.google.com. The "www." refers to the connection to the World Wide Web; the middle portion
of a domain name is usually the name of the company that owns the computer—in this case,
Google; the final portion of a domain name tells you what kind of site is served by this machine—in
this case, ‘.com’ means this is a commercial site. Other categories include: .net, .org, .edu, .fr, .uk,
etc. All devices sharing a common part of the IP address share that domain.
dotted quad:
This refers to the IP address number.The dotted quad is a unique number format made
up of four parts separated by dots. For example, 116.112.96.2.
E
ext2:
Second extended filesystem. A native filesystem for the Linux kernel. It was initially designed to
replace the extended filesystem (ext). It is fast enough that it is used as the benchmarking standard.
Although ext2 is not a journaling filesystem, its successor, ext3, provides journaling and is almost
completely compatible with ext2.
ext3:
Third Extended Filesystem. A journalled filesystem that is commonly used by the Linux
operating system. Unlike its predecessor, ext2, the journaling support alleviates lengthy filesystem
checks (fsck) at bootup after a sudden system crash, reset, or power loss. It is the default filesystem
for many popular Linux distributions.
