Additional restrictions and limitations

12/01/2021 Contributors

There are several additional restrictions and limitations when using the SnapMirror Business Continuity solution.

Consistency groups

From ONTAP 9.8 to 9.9.1, the maximum number of SnapMirror Synchronous consistency group relationships in a cluster is five, a limit which is platform-independent. Beginning in ONTAP 9.10.1, the maximum number of SnapMirror Synchronous consistency group relationships in a cluster is 20. If you reach or attempt to exceed this limit, an error message will display.

Volumes per consistency group

From ONTAP 9.8 to 9.9.1, the maximum number of volumes supported per SnapMirror Synchronous consistency group relationship is twelve, a limit which is platform-independent. Beginning in ONTAP 9.10.1, the maximum number of volumes supported per SnapMirror Synchronous relationship is sixteen. If you reach or attempt to exceed this limit, an error message will display.

Volumes

The limit is on the number of endpoints and not the number of relationships. A consistency group with 12 volumes contributes 12 endpoints on both the source and destination.A SnapMirror Synchronous relationship with both source and destination volumes on the same HA pair contributes 2 endpoints.

The maximum endpoints per platform are included in the following table.

S. No	Platform	Endpoints per HA for SM-BC		Overall sync and SM-BC endpoints per HA
		ONTAP 9.8-9.9	ONTAP 9.10.1	ONTAP 9.8-9.9	ONTAP 9.10.1
1	AFF	60	200	80	200
2	ASA	60	200	80	200

SAN object limits

The following SAN object limits are included in the following table and apply regardless of the platform.

Limits of objects in an SM-BC relationship	Count
LUNs per volume	256
LUN maps per node	2048
LUN maps per cluster	4096
LIFs per VServer (with at least one volume in an SM-BC relationship)	256
Inter-cluster LIFs per node	4
Inter-cluster LIFs per cluster	8

NTFS Security Style

NTFS security style is not supported on SM-BC volumes.

Solaris Host setting recommendation for SM-BC configuration

Beginning in ONTAP 9.10.1, SM-BC supports Solaris 11.4. In order to ensure the Solaris client applications are non-disruptive when an unplanned site failover switchover occurs in an SM-BC environment, the following setting needs to be configured on Solaris 11.4 host. This setting will override the failover module – f_tpgs in order to prevent the code path that detects the contradiction from being executed.

Follow the instructions to configure the override parameter:

Create configuration file /etc/driver/drv/scsi_vhci.conf with an entry similar to the following for the NetApp storage type connected to the host:
```
scsi-vhci-failover-override =
"NETAPP  LUN","f_tpgs"
```

Use devprop and mdb commands to verify the override has been successfully applied:

root@host-A:~# devprop -v -n /scsi_vhci scsi-vhci-failover-override scsi-vhci-failover-override=NETAPP  LUN + f_tpgs
root@host-A:~# echo "*scsi_vhci_dip::print -x struct dev_info devi_child | ::list struct dev_info devi_sibling| ::print struct dev_info devi_mdi_client| ::print mdi_client_t ct_vprivate| ::print struct scsi_vhci_lun svl_lun_wwn svl_fops_name"| mdb -k`

svl_lun_wwn = 0xa002a1c8960 "600a098038313477543f524539787938"
svl_fops_name = 0xa00298d69e0 "conf f_tpgs"

conf will be added to the svl_fops_name when a scsi-vhci-failover-override has been applied.
For additional information and recommended changes to default settings, refer to NetApp KB article Solaris Host support recommended settings in SnapMirror Business Continuity (SM-BC) configuration.

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