HP LH4r Integrated HP NetRaid Controller Configuration Guide - Page 134

Online, Hot Spare, Failed, Rebuilding, SCSI ID, Stripe Size, Stripe Width, Striping, Virtual Sizing

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Glossary • Online: a powered-on and operational disk that has been configured. • Hot Spare: a powered-on, stand-by disk ready for use should a disk fail. • Failed: errors on the disk have caused it to fail, or you have used an HP NetRAID utility to take the drive offline. • Rebuilding: a disk in the process of having data restored from one or more critical logical drives. SCSI ID: Each SCSI device on a SCSI bus must have a different SCSI address number (Target) from 0 to 15, but not 7, which is reserved for the SCSI controller. Stripe Size: The amount of data contiguously written to each disk. Also called "stripe depth." You can specify stripe sizes of 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB, for each logical drive. For best performance, choose a stripe size equal to or smaller than the block size used by your host operating system. A larger stripe depth produces higher read performance, especially if most of the reads are sequential. For mostly random reads, select a smaller stripe width. You may specify a stripe size for each logical drive. A 128-KB stripe requires 8 MB of memory. Stripe Width: The number of disk modules across which the data is striped. Equivalent to the number of disks in the array. Striping: Segmentation of logically sequential data, such as a single file, so that segments can be written to multiple physical devices in a round-robin fashion. This technique is useful if the processor is capable of reading or writing faster than a single disk can supply or accept it. While data is being transferred from the first disk, the second disk can locate the next segment. Data striping is used in some modern databases and in certain RAID devices. Virtual Sizing: This setting, when enabled for a logical drive, causes the controller to report the logical drive size as 82 GB even though the actual physical capacity is much less. The "virtual" space allows for online capacity expansion. Write Policy: When the processor writes to disk, the data is first written to the cache on the assumption that the processor will probably read it again soon. The two Write policies for HP NetRAID are: • Write Back: In a write-back cache, data is written to disk only when it is forced out of the cache. Write-back requires the cache to initiate a write to disk of the flushed entry, followed (for a processor read) by a main 128

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Glossary
128
•
Online
: a powered-on and operational disk that has been configured.
•
Hot Spare
: a powered-on, stand-by disk ready for use should a disk fail.
•
Failed:
errors on the disk have caused it to fail, or you have used an HP
NetRAID utility to take the drive offline.
•
Rebuilding
: a disk in the process of having data restored from one or
more critical logical drives.
SCSI ID
: Each SCSI device on a SCSI bus must have a different SCSI address
number (Target) from 0 to 15, but not 7, which is reserved for the SCSI
controller.
Stripe Size
: The amount of data contiguously written to each disk. Also called
"stripe depth." You can specify stripe sizes of 4 KB, 8 KB, 16 KB, 32 KB, 64
KB, and 128 KB, for each logical drive. For best performance, choose a stripe
size equal to or smaller than the block size used by your host operating system. A
larger stripe depth produces higher read performance, especially if most of the
reads are sequential. For mostly random reads, select a smaller stripe width. You
may specify a stripe size for each logical drive. A 128-KB stripe requires 8 MB of
memory.
Stripe Width
: The number of disk modules across which the data is striped.
Equivalent to the number of disks in the array.
Striping
: Segmentation of logically sequential data, such as a single file, so that
segments can be written to multiple physical devices in a round-robin fashion.
This technique is useful if the processor is capable of reading or writing faster
than a single disk can supply or accept it. While data is being transferred from
the first disk, the second disk can locate the next segment. Data striping is used
in some modern databases and in certain RAID devices.
Virtual Sizing
: This setting, when enabled for a logical drive, causes the
controller to report the logical drive size as 82 GB even though the actual
physical capacity is much less. The "virtual" space allows for online capacity
expansion.
Write Policy:
When the processor writes to disk, the data is first written to the
cache on the assumption that the processor will probably read it again soon. The
two Write policies for HP NetRAID are:
•
Write Back
: In a write-back cache, data is written to disk only when it is
forced out of the cache. Write-back requires the cache to initiate a write to
disk of the flushed entry, followed (for a processor read) by a main