Installation guide

G-2 AcceleRAID 150 Installation Guide
Disk Media Error Management
When a disk reports a media error during a read, the controller reads the data
from the mirror (RAID 1 or 0+1), or computes the data from the other blocks
(RAID 3, RAID 5), and writes the data back to the disk that encountered the
error. If the write fails (media error on write), the controller issues a
“reassign” command to the disk, and then writes the data to a new location.
Since the problem has been resolved, no error is reported to the system.
When a disk reports a media error during a write, the controller issues a
“reassign” command to the disk, and writes the data out to a new location on
the disk.
Drive Groups (or Drive Packs)
A group of individual disk drives (preferably identical) that are logically tied
to each other and are addressed as a single unit. In some cases this may be
called a drive “pack” when referring to just the physical devices. Up to eight
(8) drives can be configured together as one drive group.
All the physical devices in a drive group should have the same size,
otherwise each of the disks in the group will effectively have the capacity of
the smallest member. The total size of the drive group will be the size of the
smallest disk in the group multiplied by the number of disks in the group.
For example, if you have five disks of 400MB plus one disk of 200 MB they
are equal to six disk of 200MB of total storage. With RAID 3 or RAID 5, one
disk’s worth of storage is dedicated to parity. Therefore, the equivalent data
capacity of the array would be five disks of 200MB or 1000MB (5*200).
Hot Replacement of Disks (Hot Swap)
The design of the DAC960 Series 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), system service continues
without interruption.