cr man page on BSDOS

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CR(4)			    BSD Programmer's Manual			 CR(4)

NAME
     cr - 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 ALSO
     diskdefect(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
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