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HP StorageWorks Modular Smart Array 1000 HP StorageWorks 1000/1500 Modular Sma - Page 49

Table 6, Advantages

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B1 B2 P1,2 Q1,2 B3 P3,4 Q3,4 B4 P5,6 Q5,6 B5 B6 Q7,8 B7 B8 P7,8 D1 D2 D3 D4 15317 Figure 8 RAID 6 array, with four physical hard drives (D1, D2, D3, and D4) showing distributed parity information (Px,y)(Qx,y) This method is most useful when data loss is unacceptable, but cost is also an important factor. The probability that data loss will occur when arrays are configured with RAID 6 is less than when they are configured with RAID 5. Table 6 RAID 6 features Advantages High read performance. High data availability-Any two drives can fail without loss of critical data. More drive capacity is usable than with RAID 1+0-Parity information requires only the storage equivalent to two physical drives. Disadvantages Relatively low write performance (lower than RAID 5), because of the need to create two sets of parity data. HP StorageWorks 1000/1500 Modular Smart Array Command Line Interface user guide 49

Section	Page
Contents	3
Intended audience	7
Related documentation	7
Document conventions and symbols	7
HP technical support	9
HP-authorized reseller	9
Helpful websites	9
Overview and setup	11
About the CLI	11
CLI commands in redundant configurations	12
CLI command syntax	12
Overview of CLI storage configuration procedures	13
Accessing the CLI	14
Using the CLI	17
Help commands	17
Show commands	19
LUN-related commands	25
Flashing LEDs/locating hard drives	25
Creating LUNs	26
Assigning a name or ID to a LUN	28
Adding a spare to an existing LUN	29
Deleting LUNs	29
Deleting spares	30
Recognizing a failed unit	30
Expanding an array	30
Extending a LUN	31
Migrating a LUN to a different RAID level	31
Changing the cache setting for a LUN	32
Setting the preferred path for a LUN	32
Enabling/disabling automatic path switching	34
Global commands	35
Setting global variables	35
Setting the controller ID	36
Setting hard addressing	36
Changing the CLI prompt	37
Updating MSA firmware	37
Disabling a controller for removal	39
Overriding the ACU lock	39
Enabling or disabling debug console logging	39
Host connection commands	40
Adding a connection	40
Changing the profile of a connection	41
Changing the user-defined name of a connection	41
Deleting the user-defined name of a connection	42
Creating a new profile	42
Moving to a different profile	42
Changing the profile mode	43
Access Control List commands	43
Viewing the ACL	43
Adding to the ACL	44
Deleting information from the ACL	44
Storage overview	45
Arrays and logical drives	45
Fault-tolerance methods	46
RAID 0-No fault tolerance	47
RAID 1+0-Drive mirroring	47
RAID 5-Distributed data guarding	48
RAID 6-Advanced data guarding	48
Comparison of RAID methods	50
Choosing a RAID level	50