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Chapter 9: Glossary
Network Storage System (NSS) Administrator Guide
Chapter
9
Hotplug:
The ability to add or remove hardware without first powering down the system.
I
IEEE 802.1ad:
Protocols that provide separate instances of MAC services to multiple independent
users on a bridged LAN (local area network) in a way that does not require cooperation among the
users, but does require a minimum of cooperation between users and the MAC service provider.
IEEE 802.1p:
An IEEE standard that provides quality of service (QoS) in 802-based networks at the
MAC level. 802.1p uses three bits (defined in 802.1q) to allow switches to reorder packets based on
priority level (traffic class expediting and dynamic multicast filtering). It also defines the Generic
Attributes Registration Protocol (GARP) and the GARP VLAN Registration Protocol (GVRP). GARP
lets client stations request membership in a multicast domain, and GVRP lets them register into a
VLAN. Eight different classes of service are available, expressed through three extra bits on the
Ethernet Frame. The way traffic is treated when assigned to any particular class is undefined and left
to the implementation. The IEEE however has made some broad recommendations. 802.1p is used
within the IEEE 802.1D and IEEE 802.1Q standards.
IEEE 802.1Q:
An Ethernet, Layer 2 standard for providing VLAN identification and QoS (Quality of
Service) levels for devices on a network. This is achieved by adding four bytes to the Ethernet frame
header of a data packet (three bits of which assign up to eight priority or QoS levels and 12 bits
identify up to 4096 VLANs).
IEEE 802.1X:
Standard for port-based network access control that authenticates devices attached to
a LAN port. This standard establishes connection to a network and its connected resources if
authentication is approved, and conversely, prevents access to the network if authentication fails. An
authentication server resides in each Linksys Business Series NSS product.
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JBOD:
Just a Bunch of Disks. Multiple hard disk drives (HDDs) that are combined into a single virtual
drive. In a JBOD configured array, each drive can be a different size or capacity (this storage
method can be used to turn two or more odd-sized hard drives into one useful drive). There is no
redundancy provided with a JBOD and the failure of one disk in the array usually results in the loss
of the data stored on the JBOD.
Journaling Filesystem:
A fault-resilient filesystem that provides data integrity because updates to
directories and bitmaps are constantly written to a serial log on disk before the original disk log is
updated. If the system fails, a full journaling filesystem restores the data on the disk to its pre-crash
configuration. It also recovers unsaved data and stores it in the location where it would have gone if
the computer had not crashed. This type of system is beneficial for mission-critical systems. A
physical journal logs verbatim copies of blocks that will be written later (for example, ext3) as
compared with a logical journal that logs metadata changes in a special, more compact format.
Logical journals can improve performance by reducing the amount of data that needs to be read
from and written to the journal in large, metadata-heavy operations (for example, deleting a large
directory tree). XFS keeps a logical journal.
L
LDAP (Lighweight Directory Access Protocol):
A protocol that lets users find organizations,
workgroups, other users, network resources (such as directories, volumes, files) or peripheral devices
