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Teradata RDBMS Database Administration - NCR

NCR Teradata RDBMS Database Administration - NCR , 2004. - 616 p.
Download (direct link): teradatadatabaseadmin2004.pdf
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In-Doubt Resolution

The system performs automatic in-doubt resolution when communication is reestablished between the coordinator and participant. If the Teradata RDBMS restarts, the system must re-establish in-doubt transactions as inactive transactions (note that non-read locks are held). At some point, the coordinator must send an abort or commit request to complete the transaction.

In some situations, you may need to manually resolve in-doubt transactions. You can perform manual in-doubt resolution via the:

TPCCONS utility

TDP COMMIT and ROLLBACK commands

2PC Error Handling

Errors are handled as follows:

IF an error is detected . THEN the transaction is .
before the transaction reaches the in-doubt stage considered to be a failure and the transaction is aborted.
after the transaction reaches the in-doubt stage not aborted and recovery may be possible.

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Teradata RDBMS Database Administration 7 - 17 Chapter 7: Protecting Data

Transaction Data Protection

Hardware Data Protection

This section discusses:

Configuration of a RAID disk array

Disk array architecture

Comparison of RAID levels (1, 5, and S)

Cliques

RAID Array Configuration

RAID is a data protection scheme that uses disk arrays to protect data from a single disk failure. An array is made up of the following:

A set of disk drives attached to a disk array controller, either internally housed (mounted inside the system cabinet) or mounted in a separate cabinet

Special array software (RAID Manager) that keeps track of how data is distributed across the drives

A Disk Array Controller (DAC) cabled to a host adapter

A Redundant Disk Array Controller (RDAC) cabled to a separate host adapter

Each array controller supports four or five Small Computer System Interface (SCSI) busses (channels). On an external array, each channel can have from one to ten disks.

If the DAC or its SCSI host adapter fails, the RDAC can take over using a separate SCSI host adapter.

Disk Array Architecture

The disks of an array are organized in ranks. Each rank contains two to five disk drives, depending on model number. All the drives in one rank share a common SCSI identifier except for Model 6282 RAID 5.

Note that disks in a rank are not directly cabled to one another.

DAC, RDAC, and ranks are illustrated in the following figure.

Teradata RDBMS Database Administration

7 - 15 Chapter 7: Protecting Data

Transaction Data Protection

Differential SCSI bus

SCSI > Host

Adapters (Differential)

Single-Ended SCSI bus

i.

0

?

Rank 0 Rank 1

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Disk Array Controller

Redundant Disk Array Controller

Differential SCSI bus

RAID Manager uses drive groups. A drive group is a set of from 2 to 10 drives configured into one or more Logical Units (LUNs). All the disks in a drive group must be of the same RAID level (1, 5, or S).

The characteristics of LUNs are:

A LUN is a portion of every disk drive in a drive group.

Each LUN is configured to look like a single operating system disk.

LUNs cannot span drive groups; thus, any LUN can belong to only one drive group.

Each LUN is uniquely identified.

The pdeconfig utility slices LUNs into pdisks. To optimize performance, pdeconfig groups pdisks into virtual disks (vdisks) and assigns each vdisk to one AMP. No cabling is involved.

The following figure illustrates a sample RAID 5 setup:

HD05B001

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Teradata RDBMS Database Administration 7 - 15 Chapter 7: Protecting Data

Transaction Data Protection

AMPs (host CPUs)

CONTROLLER

? ? ? ? ?

Rank 0

LUN 0 LUN 1 LUN 2 LUN 3

Rank 1

LUN 0 LUN 1 LUN 2 LUN 3

HD05A002

Parity Segment1 Segment2 Segment3 Segment4
Segment5 Parity Segment6 Segment7 Segment8
Segment9 Segment10 Parity Segment11 Segment12
Segment13 Segment14 Segment15 Parity Segment16

HD05A003

Teradata RDBMS Database Administration

7 - 15 Chapter 7: Protecting Data

Transaction Data Protection

The pdeconfig utility slices disks differently depending on your server operating system, as follows:

IF your OS is . THEN the pdeconfig utility creates .

UNIX a LUN by including a region of space from each of the physical disks

MP-RAS in the rank. The pdeconfig default is four equal-sized LUNs per rank.

As a result, a quarter of each physical disk is assigned to each LUN.

LUNs are divided into slices as follows:

Slice Type Comment
User User slices, also called pdisks, are used for database storage. A LUN can contain 1-4 equal-sized user slices, depending on the LUN size. The maximum LUN size is 7.8 GB. The maximum user slice size is 2 GB.
Boot UNIX requires that a LUN include a boot slice. The boot slice takes up only 35 sectors.

one LUN per rank, utilizing all space on the physical disks in the rank. A maximum of eight LUNs/disk array are allowed. Each LUN is divided into four equal partitions, or pdisks, which are used for database storage.
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