IBM ServeRAID-4 Ultra160 Series, User Reference

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Selecting a RAID level and performance tuning
When selecting a RAID level for your system, consider the following:
RAID level Data
redundancy Hard disk drive
capacity utilization Read
performance Write
performance Built-in spare
drive
RAID level-0 No 100% Superior Superior No
RAID level-1 Yes 50% Very high Very high No
RAID level-1E Yes 50% Very high Very high No
RAID level-5 Yes 67% to 94% Superior High No
RAID level-5E Yes 50% to 88% Superior High Yes
RAID level-00 No 100% Superior Superior No
RAID level-10 Yes 50% Very high Very high No
RAID level-1E0 Yes 50% Very high Very high No
RAID level-50 Yes 67% to 94% Superior High No
Drive-state descriptions
This section provides descriptions of the physical and logical drive states.
ServeRAID publications frequently refer to these states during instructions and
procedures.
Physical drive-state descriptions
The following table provides descriptions of the valid physical drive states.
Drive state Meaning
Defunct A physical drive in the online, hot-spare, or rebuild state has become defunct. It does not
respond to commands, which means that the ServeRAID controller cannot communicate
properly with the drive.
If a physical drive has become defunct, refer to “Rebuilding a defunct drive” on page 147.
Hot spare A hot-spare drive is a physical drive that is defined for automatic use when a similar drive
fails.
Online The drive is online. It is functioning properly and is part of an array.
Rebuilding The drive is being rebuilt.
For more information on rebuilding a drive, refer to “Rebuilding a defunct drive” on page 147.
Ready The ServeRAID controller recognizes a ready drive as being available for definition.
Standby hot spare A standby hot spare is a hot-spare drive that the ServeRAID controller has spun down. If an
online drive becomes defunct and no suitable hot-spare drive is available, a standby
hot-spare drive of the appropriate size automatically spins up, and enters the rebuild state.
1. Disk utilization, read, and write performance depend on the number of drives in the array. Generally, the more drives in the array,
the better your performance.
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IBM
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User’s Reference: ServeRAID
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-4 Ultra160 SCSI Controller