User Manual

Introduction
1-9
logical disks can be put together to create volumes using striping,
concatenation, or both. The JBOD disks, logical disks, and volumes, are
virtual disks, which can be exported to host interfaces as SCSI logical units
(LUN) and serve I/O access from the host systems. Below are more
descriptions about each storage objects.
• JBOD disk
A JBOD (Just a Bunch Of Disks) disk is formed by single hard disk that can
be accessed by hosts as a LUN exported by the controller. The access to
the LUN is directly forwarded to the hard disk without any address
translation. It is often also named as pass-through disk.
• Member disk
The hard disks in a disk group are member disks (MD). A member disk of a
disk group can be a data disk or a local spare disk. A data member disk
provides storage space to form logical disks in a disk group.
• Disk group
A disk group (DG) is a group of hard disks, on which logical disks can be
created. Operations to a disk group are applied to all hard disks in the
disk group.
• Logical disk
A logical disk (LD) is formed by partitioning the space of a disk group.
Logical disks always use contiguous space, and the space of a logical
disk is evenly distributed across all member disks of the disk group. A
logical disk can be exported to hosts as a LUN or to form volumes.
• Local spare and global spare disk
A spare disk is a hard disk that will automatically replace a failed disk and
rebuild data of the failed disk. A local spare disk is dedicated to single
disk group, and a global spare disk is used for all disk groups. When a disk
in a disk group fails, the controller will try to use local spare disks first, and
then global spare disks if no local spare is available.
• Volume
A volume is formed by combining multiple logical disks using striping
(RAID0) and concatenation (NRAID) algorithms. Multiple logical disks form
single volume unit using striping, and multiple volume units are
aggregated to form a volume using concatenation. A volume can be
exported to hosts as a LUN.
• Logical unit
A logical unit (LUN) is a logical entity within a SCSI target that receives
and executes I/O commands from SCSI initiators (hosts). SCSI I/O
commands are sent to a target device and executed by a LUN within the
target.