Mylex DAC960PG, Руководство по установке

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Glossary
Glossary-2 DAC960PG Installation Guide
Disk Failure Detection
The controller automatically detects SCSI disk failures. A monitoring
process running on the controller checks, among other things, elapsed time
on all commands issued to disks. A time-out causes the disk to be “reset”
and the command to be retried. If the command times out again, the disk
could be “killed” (taken “offline”) by the controller (its state changed to
“dead”). DAC960PG controllers also monitor SCSI bus parity errors and
other potential problems. Any disk with too many errors will also be ‘killed’.
Disk Media Error Management
DAC960PG controllers transparently manage SCSI disk media errors. Disks
are programmed to report errors, even ECC-recoverable errors. If ECC EDO
RAM is installed, the controller will correct ECC errors.
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 4 disks of 400MB each, and 1 disk of 200MB in a
pack, the effective capacity available for use is only 1000MB (4*200), not
1800MB.