Direct Storage Access

When using "Direct Storage Access", Veeam summarizes VMware's VDDK based "Direct SAN" mode, and Veeam's proprietary "Direct NFS".

The Direct SAN mode uses a direct data path (Fibre Channel or iSCSI) between the VMFS datastore and the backup proxy for data transfer. The proxy needs at least read access to the datastores so Fibre Channel zoning, Networking and LUN masking on the storage need to reflect this.

To use Direct NFS backup mode, the proxies need access to the NFS network and need to be member of the NFS storage server's "export policy" for read and/or write access.

Pros

• Direct Storage Access mode provides very fast and the most reliable predictable backup performance (typically, using 8 Gb Fibre Channel or 10 GbE for iSCSI and NFS).
• Produces zero impact on vSphere hosts and VM production networks for backup data transport.
• It is also possible to perform full VM restore using Direct Storage Access. This mode will be used automatically if eligible backup proxies are available in the backup infrastructure, and the VM disks are thick provisioned.
• Direct Storage Access is the fastest backup and restore mode for NFS datastores. It uses multiple concurrent read and write streams with an increased queue depth.
• Direct Storage Access for NFS datastores will mitigate the "VM stun" issues that may be caused by Virtual Appliance Mode (hot-add).
• Direct Storage Access for FC and iSCSI can be used for replication at the target for the initial replication (with thick provisioned disks) only. For NFS datastores, Direct Storage Access can be used for initial and incremental replication passes. There are no differences on the source replication proxy.

Cons

• Typically Direct Storage Access requires a physical server for Fibre Channel, iSCSI or NFS connection. For virtual only deployments, Direct Storage Access for iSCSI and NFS is possible, but would transport the data through networks of the ESXi hosts.
• Restore via Direct Storage Access using Fibre Channel or iSCSI is possible only for thick-provisioned VM disks. At restore the data stream needs to be coordinated in the background with vCenter or an ESXi host which can slow down the restore speed. Consider adding additional hot-add proxy servers for restore (FC/iSCSI only).
• Direct SAN mode (FC/iSCSI only) is the most difficult backup mode to configure as it involves reconfiguring not only the storage but also the SAN, (Fibre Channel Zoning, LUN masking, or reconfiguration of iSCSI targets) to provide the physical proxy server(s) with direct access to the production VMFS datastores. When such configuration has been implemented it is extremely important to ensure that HBAs, NIC drivers and firmwares are up-to-date and that multi path driver software (e.g. MPIO) is properly configured.

For more information about configuring Direct Storage Access refer to FAQ at Veeam Community Forums: Direct Storage Access Mode

Example

If datastores or virtual raw device mapping (vRDM) LUNs are connected via shared storage using Fibre Channel, FCoE or iSCSI, you may add a backup proxy as a member to that shared storage using LUN masking. This will allow for accessing the storage system for backup and restore.

Ensure that a connection between the storage and backup proxy can be established. Verify FC HBAs, zoning, multipath, driver software and iSCSI configurations including any network changes. To test the connection it is best practices to count the volumes at windows disk manager adding one disk per storage system at a time. Later add all the others. This will streamline the search for errors.

Recommendations

• Use the multipath driver software of the storage vendors choice (preferred integration into Microsoft MPIO) to avoid disk or cluster failovers at storage level. This will also prevent the whole storage system from being affected by possible failovers if wrong data paths are used. It is highly recommended to contact the storage vendor for optimal settings.
• If you attach a great number of volumes to the backup proxy consider that logging and search for the correct volume at the job run can require extra processing time per VM disk (as well as for overall volume count). To avoid this, the Veeam logging of the particular process can become the bottleneck you can disable this with the registry setting
  • Path: HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup and Replication
  • Key: VDDKLogLevel
  • Type: REG_DWORD
  • Value: 0
  • Default: 1

  Note: As this reduces the amount of information in debug logs remember to enable it again when working with Veeam support (to facilitate debugging of the Direct Storage Access-related challenges).

  Security Considerations for Direct SAN mode with FibreChannel or iSCSI

  During deployment of the proxy role to a Windows VM, Backup & Replication uses the following security mechanisms to protect them:

  • Changes the Windows SAN Policy to "Offline (shared)". This prevents Windows from automatically bringing the attached volumes online and also prevents Windows write operations to the volumes. During Direct SAN restore, if the disks are offline, the proxy will attempt bringing the volume online, and verify that it is writeable. In case the operation fails, restore will failover to using NBD mode through the same proxy.
  • Veeam deploys VMware's VDDK Kit into the backup proxy server, in most cases this VDDK Kit coordinates read and write processes (Direct SAN restore) with VMware vSphere allowing VMware's Software to control the read and write streams in a reliable manner.

  If necessary you can take additional measures as follows:

  • Disable automount. Open a command box and type "diskpart". Then disable automaount with "automount disable".
  • Disable Disk Management snap-in with: Group Policy\User Configuration > Administrative Templates > Window > Components > Microsoft Management Console > Restricted/Permitted snap-ins > Disk Management.
  • Avoid providing excessive administrative access to the account used to run Veeam proxy servers.
  • Present LUNs as read-only to the backup proxy server. This capability is supported by most modern storage. When possible implement read-only LUN masking on the storage system or read-only zoning on the Fibre Channel switches (possible on most Brocade variants).

  If a VMFS datastore is manually brought online in Windows Disk Management by mistake, and disk resignaturing is initiated, the datastore will become unavailable, and VMs will stop. Please contact VMware Support for assistance with recreating the VMFS disk signature. For more information on Windows re-signaturing process and VMware datastores please refer to VMware KB1002168: Unable to access the VMware virtual machine file system datastore when the partition is missing or is not set to type fb

  Summary

  Use Direct Storage Access whenever you have the chance to do so for fast backup speed and reduced load on the ESXi host. For fibre channel and iSCSI based datastore it processes backup data reliably and very fast. Consider using HotAdd proxies as these restores are much faster than Direct SAN restores. Direct SAN uses VDDK which can cause excessive metadata updates while hot-add restore bypasses VDDK.

  For NFS datastores Veeam's Direct NFS mode is the mode you should choose for backup and restore as it delivers top speed without any negative side effects. You can use it for virtual and physical proxy deployments.

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