Alignment Values

The disk group block alignment has two values: 1 block or 8k (8 kilobytes).

Alignment Value 1

All disk group versions before version 110 must have a alignment value of 1.

Disk groups have an alignment value of 1 after upgrading from pre-version 110 to version 110 or later.

Encapsulated disks, which require disk cylinder alignment, have an alignment value of 1.

Non-CDS disk groups version 110 and later can have either a value of 1 block or 8k.

Alignment Value 8K

Non-CDS disk groups version 110 and later can have either a value of 1 block or 8k.

All CDS disk groups have an alignment value of 8k.

The alignment for all newly initialized disk groups in VxVM 4.0 or a later release is 8k. This value (which is used when creating the disk group) cannot be changed. However, the disk group alignment can be subsequently changed (refer to Changing the Alignment of a Non-CDS Disk Group).

Dirty Region Log (DRL) Alignment

The location and size of each map within a Dirty Region Log (DRL) must not violate the disk group alignment for the disk group (containing the volume to which the DRL is associated). This means that the region size and alignment of each DRL map must be a multiple of the disk group alignment, which for CDS disk groups is 8K. (Features utilizing the region size can impose additional minimums and size increments over and above this restriction, but cannot violate it.)

In a version 110 disk group, a traditional DRL volume must have:

• Minimum region size of 512K
• Incremental region size of 64K

In a version 110 disk group, a version 20 DCO volume must have:

• Minimum region size of 16K
• Incremental region size of 8K

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  Note    The map layout within a Data Change Object (DCO) volume changed with the release of VxVM 4.0 to version 20. This can accommodate both FastResync and DRL maps within the DCO volume. The original version 0 layout for DCO volumes only accommodates FastResync maps.

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