Compound Rules

Whether a rule applies to a volume, mirror, column or log depends on the scope in which the rule is applied. Compound rules are composed of several other rules, and are used to specify the scope of rules at a level below that of an entire volume. A compound rule can apply to one or more mirrors, columns or logs of a volume. It can also define how redundancy and separation are to be implemented for a volume.

The following sections describe the various types of compound rule:

• mirror
• mirror_group
• stripe
• log

mirror

The mirror rule is used to describe one or more mirrors of a volume. All the basic rules except striped and parity, and a restricted form of the stripe rule, can be used within a mirror rule. Rules that are specified within a mirror rule apply only to those mirrors that are constructed from this rule.

The following examples demonstrate the application of the mirror rule:

• Confine each mirror within an enclosure so that no mirror spans more than one enclosure:

mirror all {
  confineto "Enclosure"
}
• Configure two mirrors of a volume with the EMCSnapshot feature:

mirror 2 {
  apply EMCSnapshot
}
• Use confineto rules to force one mirror to be created on each of four separate enclosures:

mirror 1 {
  confineto "Enclosure"="enclr1"
}
mirror 1 {
  confineto "Enclosure"="enclr2"
}
mirror 1 {
  confineto "Enclosure"="enclr3"
}
mirror 1 {
  confineto "Enclosure"="enclr4"
}

mirror_group

The mirror_group rule groups together different mirrors of a volume. It should be used when there are groups of mirrors with several things that are common to each group, or when such groups need to have a separateby rule between them. Merging of mirrors can only take place within mirror groups.

The following example demonstrates the application of the mirror_group rule:

• Configure two mirror groups, A with two striped mirrors, and B with two concatenated mirrors, where the mirrors in each group lie within different enclosures:

mirror_group A {
  mirror 2 {
   confineto "Enclosure"
  }
  stripe 4
}

mirror_group B {
  mirror 2 {
   confineto "Enclosure"
  }
  striped false
 }

mirror_group A,B {
  separateby "Enclosure"
}

stripe

The stripe rule describes one or more columns of a volume. All basic rules and some restricted form-related or mirror-related rules can be specified within a stripe rule. ISP merges multiple stripe rules to form a single stripe rule whose rules are the union of the separate stripe rules.

The following examples demonstrate the application of the stripe rule:

• Stripe a VxVM object over 5 columns:

stripe 5
• Use confineto rules to force a column to be created on separate enclosures, but which are attached to the same controller, ctlr1:

stripe 6-2 {
  confineto "Controller"="ctlr1"
  separateby "Enclosure"
}

Six columns are created by preference. If this is not possible, ISP attempts to create fewer columns down to a minimum of two.

log

The log rule describes a volume's logs. The argument of the rule specifies how many mirrors the log should have. Compound rules can include storage selection rules, stripe rules, and define the log type. The following log types may be defined:

dco Version 20 data change object (DCO) that can be used for both DRL and FastResync.

raid5 RAID-5 log.

The following examples demonstrate the application of the log rule:

• Create a striped RAID-5 log with 4 columns, and a DCO log, each of which are confined to LUNs from a single (but possibly separate) enclosure:

parity true
log 1{
  type raid5
  confineto "Enclosure"
  stripe 4
}
log 1{
  type dco
  confineto "Enclosure"
}
• Create a mirrored new-style DCO log, with each plex configured on a separate controller.

mirror 2
log 2{
  type dco
  separateby "Controller"
}