What is ‘Atleast resource dependency’?
Atleast resource dependency is useful where parent resource depends on multiple child resources but parent resource does not require all child resources to be online before parent resource comes online.
E.g. Let’s consider one parent resource ‘p’ which has ‘x’ number of child resources. When we link resource ‘p ‘with ‘x’ child resources using traditional VCS resource dependency, in such case ‘p’ can come online only when all ‘x’ child resources are online. This may restrict the functionality of ‘p’ resource where it does not require all child resources to be online when parent comes online. To overcome such restriction VCS has introduced ‘Atleast resource dependency’ which is available from VCS 6.2 onwards.
In Atleast resource dependency, resource ‘p’ can be linked with ‘x’ resources but ‘p’ resource can come online when ‘y’ number of resources(out of x) are online, it does not wait for all ‘x’ resources to be online.
This dependency can be useful for a case where nfs and share type of resources are configured.
Note: [In following configuration we are more focused on dependency between ip and share (share1, share2…etc.) resources.]
Traditional VCS resource dependency
In the below configuration, the NFS server is configured in VCS to provide highly available NFS shares. (Refer to the Veritas Cluster Server Bundle Agent Guide to know more about configuring NFS and Share resources). The resources in the service group are linked using traditional VCS resource dependency. All the resources have “Critical” attribute set to 0.
# hares -link ip share1
# hares -link ip share2
# hares -link ip share3
# hares -link ip share4
# hares -link ip share5
Snippet 1
Resources dependency view from CLI:
# hares -dep
#Group Parent Child
nfs_grp ip share1
nfs_grp ip share2
nfs_grp ip share3
nfs_grp ip share4
nfs_grp ip share5
nfs_grp ip proxy
nfs_grp lockmount lockvol
nfs_grp lockvol diskgroup
nfs_grp mount vol
nfs_grp nfsrestart_L nfs
nfs_grp nfsrestart_L mount
nfs_grp nfsrestart_L lockmount
nfs_grp nfsrestart_U ip
nfs_grp share1 nfsrestart_L
nfs_grp share2 nfsrestart_L
nfs_grp share3 nfsrestart_L
nfs_grp share4 nfsrestart_L
nfs_grp share5 nfsrestart_L
nfs_grp vol diskgroup
Drawbacks of using “Traditional resource dependency”:
1. User will not be able to offline single child resource
# hares -offline share1 -sys vcslx325
VCS WARNING V-16-1-10287 Online resources depend on resource share1. Take them offline first
2. Parent resource (ip resource) would not come online unless all child resources (share1, share2….etc.) are online.
3. If share1 resource goes into faulted state, VCS would offline all the parent resources (‘ip’ & ‘nfsrestart_U’) causing clients to lose access to the other shares (Refer snippet 2).
Snippet 2
How to solve the above challenges using Atleast resource dependency?
The existing configuration is now modified to use Atleast dependency between the IP and Share resources. The criteria of minimum 1 share resource to be available are set for the parent resource to be online.
Example:
# hares -link ip share1,share2,share3,share4,share5 -min 1
Snippet 3
Resources dependency view from CLI:
# hares -dep -atleast
#Group Parent Child
nfs_grp ip share1, share2, share3, share4, share5. Min = 1
nfs_grp ip proxy
nfs_grp lockmount lockvol
nfs_grp lockvol diskgroup
nfs_grp mount vol
nfs_grp nfsrestart_L nfs
nfs_grp nfsrestart_L mount
nfs_grp nfsrestart_L lockmount
nfs_grp nfsrestart_U ip
nfs_grp share1 nfsrestart_L
nfs_grp share2 nfsrestart_L
nfs_grp share3 nfsrestart_L
nfs_grp share4 nfsrestart_L
nfs_grp share5 nfsrestart_L
nfs_grp vol diskgroup
Benefits of using “Atleast resource dependency”:
1. User can offline single child resource (refer snippet 4).
# hares -offline share1 -sys vcslx325
Snippet 4
2. Parent resource (ip resource) would come online when any one child resource is online, IP resource will not wait all child resources (share2, share3….etc.) to come online (refer snippet 5).
Snippet 5
3. If share1 resource goes into faulted state, VCS would not offline the parent resources ( ‘ip’ & ‘nfsrestart_U’) . The shares exported from the other resources which are online would still be accessible to clients. (Refer snippet 6).
Snippet 6
Note: [All snippets are captured from VCS java GUI]
How to link resources using Atleast dependency?
Atleast resource dependency can be created via CLI using following command
hares -link <parent res> <child res>[,<child res>,<child res>,... -min <minimum>]
E.g. # hares -link ip share1,share2,share3,share4,share5 -min 1
Note: Minimum criteria can vary between 1 & less than number of child resources.
How to unlink resources?
Resources can be unlinked via CLI using following command
hares -unlink <parent res> <child res>[,<child res>,<child res>,...]
E.g. # hares -unlink ip share1,share2,share3,share4,share5
