HP BL680c XenServer Administrator's Guide 4.1.0 - Page 22

Shared NetApp Storage

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Storage The sr-probe command should be used to list the LUN-backed SCSI devices present on the host, and will force a scan for new LUN-backed SCSI devices each time it is run. The path value returned by sr-probe for a LUN-backed SCSI device will be consistent across all hosts with access to the LUN, and therefore must be used when creating shared SRs accessible by all hosts in a resource pool. The same features apply to QLogic iSCSI HBAs. See Section 3.3.1, "Creating Storage Repositories" for details on creating shared HBA-based FC and iSCSI SRs. Note XenServer Host support for Fibre Channel has the following restrictions: • Dual Multipath is not supported • Direct mapping of a LUN to a VM is not supported. HBA-based LUNs must be mapped to the host and specified for use in an SR. VDIs within the SR are exposed to VMs as standard block devices. 3.2.6. Shared NetApp Storage If you have access to a Network Appliance™ (NetApp) filer with sufficient disk space, running a version of Data ONTAP 7G (version 7.0 or greater), you can configure a custom NetApp storage repository for VM storage on your XenServer deployment. The XenServer driver uses the ZAPI interface to the filer to create a group of FlexVols which correspond to an SR. VDIs are created as virtual LUNs on the filer, and attached to XenServer Hosts using an iSCSI data path. There is a direct mapping between a VDI and a raw LUN without requiring any additional volume metadata. Thus, at a logical level, the NetApp SR is a managed volume and the VDIs are the LUNs within the volume. VM cloning uses the snapshotting and cloning capabilities of the filer for data efficiency and performance and to ensure compatibility with existing ONTAP filer management tools. As with the iSCSI-based SR type, the NetApp driver also uses the built-in software initiator and its assigned server IQN, which can be modified by changing the value shown on the General tab when the storage repository is selected in XenCenter. The simplest way to create NetApp SRs is with XenCenter. See XenCenter Help for details. They can also be created using xe CLI commands. See Section 3.3.8, "Creating a shared NetApp SR over iSCSI " for an example. FlexVols NetApp introduces a notion of FlexVol as the basic unit of manageable data. It is important to note that there are limitations that constrain the design of NetApp-based SRs. These are: • maximum number of FlexVols per filer • maximum number of LUNs per network port • maximum number of snapshots per FlexVol Precise system limits vary per Filer type, however as a general guide, a FlexVol may contain up to 200 LUNs, and provides up to 255 snapshots. Since there is a one-to-one mapping of LUNs to VDIs, and often a VM will have more than one VDI, it is apparent that the resource limitations of a single FlexVol can easily be reached. Also consider that the act of taking a snapshot includes snapshotting all the LUNs within a FlexVol and that the VM clone operation indirectly relies on snapshots in the background as well as the CLI-based VDI snapshot operation for backup purposes. 16

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Storage
16
The
sr-probe
command should be used to list the LUN-backed SCSI devices present on the host, and will
force a scan for new LUN-backed SCSI devices each time it is run. The path value returned by
sr-probe
for
a LUN-backed SCSI device will be consistent across all hosts with access to the LUN, and therefore must
be used when creating shared SRs accessible by all hosts in a resource pool.
The same features apply to QLogic iSCSI HBAs.
See Section 3.3.1, “Creating Storage Repositories” for details on creating shared HBA-based FC and iSCSI
SRs.
Note
XenServer Host support for Fibre Channel has the following restrictions:
•
Dual Multipath is not supported
•
Direct mapping of a LUN to a VM is not supported. HBA-based LUNs must be mapped to the host
and specified for use in an SR. VDIs within the SR are exposed to VMs as standard block devices.
3.2.6. Shared NetApp Storage
If you have access to a Network Appliance
™
(NetApp) filer with sufficient disk space, running a version
of Data ONTAP 7G (version 7.0 or greater), you can configure a custom NetApp storage repository for
VM storage on your XenServer deployment. The XenServer driver uses the ZAPI interface to the filer to
create a group of
FlexVols
which correspond to an SR. VDIs are created as virtual LUNs on the filer, and
attached to XenServer Hosts using an iSCSI data path. There is a direct mapping between a VDI and a
raw LUN without requiring any additional volume metadata. Thus, at a logical level, the NetApp SR is a
managed volume and the VDIs are the LUNs within the volume. VM cloning uses the snapshotting and
cloning capabilities of the filer for data efficiency and performance and to ensure compatibility with existing
ONTAP filer management tools.
As with the iSCSI-based SR type, the NetApp driver also uses the built-in software initiator and its assigned
server IQN, which can be modified by changing the value shown on the General tab when the storage
repository is selected in XenCenter.
The simplest way to create NetApp SRs is with XenCenter. See XenCenter Help for details. They can also
be created using xe CLI commands. See Section 3.3.8, “Creating a shared NetApp SR over iSCSI ” for
an example.
FlexVols
NetApp introduces a notion of FlexVol as the basic unit of manageable data. It is important to note that there
are limitations that constrain the design of NetApp-based SRs. These are:
•
maximum number of FlexVols per filer
•
maximum number of LUNs per network port
•
maximum number of snapshots per FlexVol
Precise system limits vary per Filer type, however as a general guide, a FlexVol may contain up to 200
LUNs, and provides up to 255 snapshots. Since there is a one-to-one mapping of LUNs to VDIs, and often a
VM will have more than one VDI, it is apparent that the resource limitations of a single FlexVol can easily be
reached. Also consider that the act of taking a snapshot includes snapshotting all the LUNs within a FlexVol
and that the VM clone operation indirectly relies on snapshots in the background as well as the CLI-based
VDI snapshot operation for backup purposes.