CR(4) BSD Programmer's Manual CR(4)NAMEcr - Compaq RAID controller disk driver
SYNOPSIS
cr* at crc? drive ?
DESCRIPTION
This is a driver for disks on the following Compaq Array controllers:
1. Compaq Smart-2 EISA Controller
2. Compaq Smart-2 PCI Controller
3. Compaq Smart-2SL PCI Controller
4. Compaq Smart-2DH PCI Controller
5. Compaq Smart-221 PCI Controller
6. Compaq Smart-3100ES PCI Controller
7. Compaq Smart-3200 PCI Controller
8. Compaq Integrated Array
9. Compaq Smart Array 4200
10. Compaq Smart Array 4250ES
This driver must be a child of the crc controller driver.
The disks on the Compaq Array controller are logical disks, which are
part of a drive array. Drive Array technology distributes data across a
collection of physical drives into one or more logical drives. The logi-
cal drives can be configured using the Compaq Array Configuration Utili-
ty.
Compaq Array Controllers support the following options for data redundan-
cy :
1. Redundant Array of Inexpensive Disks(RAID)
2. Online Spare
3. Array Accelerator
The follwing RAID configurations are supported:
1. RAID 5
2. RAID 4
3. RAID 1
4. RAID 0
RAID-5 : Distributed data guarding.
RAID - 5 stores parity data. The parity data in the drives are used to
reconstruct the data when one of the physical drives fail. This allows
the system to continue operating with a slightly reduced performance un-
til failed drive is replaced.
This array configuration requires minimum of three physical drives and
allows a maximum of 14 drives, considering seven drives each on ports 0
and 1. Effective usage will be 33 percent of total hard drive capacity
with 3 drives and 7 percent with 14 drives.
RAID-4 : Data guarding.
RAID - 4 Assures data reliability while using only a small percentage of
the logical drive storage capacity. A designated, single drive contains
the parity data. If a drive fails, the controller uses the data on
the parity drive and the data on the remaining drives to reconstruct da-
ta from the failed drive. This allows the system to continue operating
until failed ones are replaced.
This array configuration requires minimum of three physical drives and
allows a maximum of 14 drives, considering seven drives each on port 0
and 1. Effective usage will be 33 percent of total hard drive capacity
with 3 drives and 7 percent with 14 drives.
Smart-2 array controller supports RAID-4 for backward compatibility.
RAID-5 provides the same benefits with higher performance, it's recom-
mended to use RAID-5 instead of RAID-4.
RAID-1 : Drive Mirroring.
RAID - 1 is the configuration offering fault tolerance protection that
can be configured with a minimum of two physical drives. RAID 1 always
requires an even number of drives. If a drive fails, the mirror drive
provides a backup copy of the data and normal system operations are not
interrupted.
RAID - 0 :- No Fault tolerance.
RAID 0 does not provide fault tolerance. This level of RAID stripes the
data across all the drives of the array, but it does not incorporate a
method to create redundant data. On physical drive failure data can not
be recovered.
As the drives are not used for redundant data it offers best processing
speed and capacity, for non-critical data.
On Line spare :
One or more physical drives can be configured as Online Spare for a
drive array. These drives are used to rebuild the data when a physical
drive in the array fails. The online spare drive effectively replaces the
failed drive.
The online spare improves the overall system fault tolerance by automat-
ically replacing a failed drive and quickly restoring the system to full
RAID fault tolerance protection.
The user can configure upto four physical drives as online spares for
each Compaq Array controller.
To provide an online spare, you must have at least one installed but
unassigned physical drive and the drive array must not have any logical
drive without fault tolerance (RAID 0).
Array Accelerator :
Compaq Array controllers are provided with cache array accelerator for
Smart-2 PCI, Smart-2 EISA and Smart-2DH controllers.
The array accelerator improves performance on data access to the drive
array by serving as write and read-ahead cache.
The array accelerator is backed up with on-board batteries, insuring that
the cached data is safe even with controller failure or power outage. The
cached data stored on the array accelerator can be moved to another array
controller. The array accelerator transfers the cached data to the drive
array.
FILES
/dev/cr[0-128][a-h]
Block device files
/dev/rcr[0-128][a-h]
Raw device files
SEE ALSOdiskdefect(8), disksetup(8,) crc(4)HISTORY
The cr driver is a recent driver supported, added in BSD/OS 3.0.
BSDI BSD/OS January 15, 1998 3