HP-UX Reference (11i v1 00/12) - 4 File Formats (vol 8)

__________________________________________________________________________________________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________________________________________________________________________________________
STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man4/!!!intro.4
________________________________________________________________
___ ___
a
arraytab(4) arraytab(4)
RAID_3: This level uses byte striping across a set of n drives, with an additional drive maintaining an
XOR parity check byte for each byte of data. The resulting logical disk sector size is n times
the sector size of one disk. Data can be recovered, if a drive fails, by using the redundancy of
the parity drive while operating in a ‘‘degraded’’ mode. Since reads and writes to the indivi-
dual mechanisms are accomplished in parallel, long I/O requests to the array complete in 1/nth
the time, exclusive of the access time, allowing higher bandwidth I/O rates. Because the
mechanisms operate in concert during the input/output operation, only one I/O may process at
a time. Disks configured in RAID_3 have access time characteristics of a single disk, but are
capable of transferring data at higher rates. This mode is most useful with long I/O requests.
RAID_5: This level uses block striping across a set of n drives. XOR parity information is maintained
across the set of the drives on a block basis, such that the failure of any one drive allows con-
tinued operation in a ‘‘degraded’’ mode. While degraded, data from the failed drive is recon-
structed from the parity information, and the data on the remaining disks. Unlike RAID_3,
block sizes can be the same as for a single disk; however, write performance suffers when
write requests are less than n blocks, because read-modify-write operations must be done on
the data drive, and the parity drive. Because the XOR parity data is maintained on a block
basis, drive mechanisms can operate independently, allowing multiple I/O requests to process
concurrently on the set of disks. This mode is most useful for short I/O requests. This mode
allows parallel processing of I/Os requests across the set of disks, however data transfer rates
are equivalent to those of a single disk.
CONFIGURATION TABLE
Entries in the configuration table are formed from a number of fields, each terminated by a ‘‘:’’ character.
The fields are organized as shown below:
Drive Group Name (Physical Configuration Name)
Drive List
...
Drive List
Logical Configuration Name
Logical partition configuration
Logical partition configuration
...
Logical partition configuration
Each part of the specification is terminated by a ’New Line’ character. The fields are generally composed of
an identifier token, followed by parameter value or values, separated by ‘‘#’’. Comments may also be placed
within the file by leading the field with ‘‘#’’. All following characters up to ’New Line’ will be ignored. A
character may be escaped by immediately preceding it with ‘‘\’’. Logical configurations and physical
configurations may appear in any order, provided the syntax requirements are met. Physical disk
configuration labels must be unique within the table. Logical configuration labels need not be unique.
However, configurations with non-unique labels should have different parameter values for the array con-
troller type field, or specify a different disk group. Logical disk configurations are searched sequentially—
the first labeled specification which matches will be used. The following list describes the arraytable
parameters and their use.
Name Type Description
ct str Array Controller Type. This parameter must be specified in at least one logical partition of a
logical configuration. The field consists of the concatenated vendor ID and product ID strings
which are returned by the SCSI Inquiry message to the array controller, with ‘‘_’’ separating
these two strings. This field defines array product for which this configuration may be used.
For example, HP_C2425D or HP_C2430D. dl num Physical Drive list. Each drive
group consists of 1 or more lists of disk mechanisms, each specified by the array channel
number, the channel ID of the disk mechanism on the channel, and a disk identifier label,
respectively. A drive list may have up to 5 drives listed. The order of the drives in the list
determines the order in which data is placed on the drives. This order is defined by the drive
Section 4−−22 − 2 − HP-UX Release 11i: December 2000
___
___