Hitachi Simple Modular Storage 100, User Manual

Page: 21 / 100

Introduction
1–7
Hitachi Simple Modular Storage 100 User’s Guide
Concepts and Terms
This section describes key concepts and terms you will find helpful when
using your Hitachi Simple Modular Storage 100. For additional assistance, a
Glossary at the back of this guide defines the technical terms in this guide.
RAID 6
Drives in your Hitachi Simple Modular Storage 100 are preconfigured for
RAID 6. RAID 6 is an extension of the RAID 5 array, with a second
independent distributed parity scheme. Data and parity are striped on a
block level across multiple array members, and a second set of parity is
calculated and written across all drives. In this way, RAID 6 delivers
enhanced data protection compared with single-parity RAID systems by
allowing for two simultaneous drive failures without downtime or data loss.
Your Hitachi Simple Modular Storage 100 supports RAID 6 in 6-, 8-, or 12-
drive configurations:
• For arrays with six drives, four drives are used for data and two are
used for parity.
• For arrays with eight drives, six drives are used for data and two are
used for parity.
• For arrays with 12 drives, 9 drives are used for data, two are used for
parity, and one acts as a spare in case one of the other drives fails.
iSCSI
Your Hitachi Simple Modular Storage 100 is an iSCSI storage device. iSCSI
(pronounced “eye skuzzy”) is an IP-based protocol that leverages the low
cost and familiarity of Ethernet and IP networking.
iSCSI links data storage devices over standard Ethernet-based TCP/IP
networks using small computer system interface (SCSI) commands.
Because iSCSI uses the standard Ethernet infrastructure to provide access
to storage “targets,” it is compatible with, and can connect directly to,
standard Gigabit Ethernet switches and IP routers. In this way, iSCSI
enables low-cost storage access through the mature and predominant
Ethernet infrastructure.
iSCSI Initiators and Targets
iSCSI defines a SCSI encapsulation protocol across a TCP/IP connection. As
with SCSI, there are two types of components in an iSCSI system: initiators
and targets.
An iSCSI initiator is a hardware device — such as an iSCSI host bus adapter
(HBA) or TCP/IP offload engine (TOE) — and/or software installed in a
server. The iSCSI initiator is the source of iSCSI commands that are sent
over the network to the target. As such, it is responsible for:
• Originating iSCSI requests for target discovery and target connection.
• Creating the iSCSI packets.