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SAN Device Virtualization. Commands hidden in NX-OS 5.x as feature has been deprecated after NX-OS 4.x. About SAN Device Virtualization (SDV). What is SAN Device Virtualization? Virtualization of Initiators/Targets

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san device virtualization

SAN DeviceVirtualization

Commands hidden in NX-OS 5.x as feature has been deprecated after NX-OS 4.x

about san device virtualization sdv
About SAN Device Virtualization (SDV)
  • What is SAN Device Virtualization?

Virtualization of Initiators/Targets

    • Target Migration = Migrating from one target (Primary Target) to another (Secondary Target) for one or more initiators (servers).
    • Server Migration = Migrating from one initiator to another for one or more targets (disk).
    • Main Focus of presentation on Target Migration, but applies to Server Migration also.
  • What is driving the need for Target Virtualization functionality?
    • Target failures: hardware, logical corruption
    • Data migration: technology refresh, workload balancing, storage consolidation
    • Virtualization Ready: for future needs
about sdv continued
About SDV continued
  • What are the benefits of the feature compared to manual migration?
    • Reduce the amount of time for migration; hence reducing the downtime
    • Ease of management; Reduces possibility of human errors.
    • Easily scalable for larger number of initiators/targets.
today s deployment for handling target failures
Today's Deployment for Handling Target Failures
  • Designed for HA; Redundancy is the key.
  • Deploy two arrays: primary & secondary.
  • Use some type consistency technology such as EMC SRDF between primary and secondary to ensure that secondary is a mirrored copy of the production LUN.
  • When primary fails, manually bring secondary online. All I/O will now take place with the secondary.
    • The time required to `use’ secondary is the problem.

Primary Target

I/O - Normal




I/O - After Primary Failure

Secondary Target

the challenges of handling target failures
The Challenges of Handling Target Failures
  • The time required to make secondary target accessible can be quite long. This impacts the application availability.
    • For a typical production environment of 2 clustered hosts, and a database size of 2TB, this takes over 4 hours.
  • This down-time consists of two components:
    • - Zoning Changes
      • All the initiators now have to be re-zoned with the Secondary Target
    • - Re-configuring certain initiators
      • Since WWN and FCID of the secondary is different, some driver files have to be changed and server rebooted, which adds risk (Eg: HP-UX and AIX servers)
      • Clustering (multiple initiators) compounds the problem; Procedure has to be repeated for each server of the cluster.

Up to a couple of hours

Zoning Changes

Changes to Initiators


Array online


Array fails

the sdv manager
The SDV Manager
  • SDV is a conditional service running on the MDS Switch Supervisor that can create virtualized devices.
  • SDV presents a Virtual (Proxy) target to initiator.
    • Initiators are presented with a Virtual Device (VD);the virtualized form of the real target.
    • VD is created by configuration and is identified by a name.
    • VD virtualizes a single real target at any point of time.
    • VD registered with Name Server with a pWWN and consumes an FCID outside of the real domain.
    • VD is ‘hosted’ by one of the switches in the fabric.
    • Administrators Zones VD with (real) initiators using regular Zoning Config. Initiator can be a VD also.
    • Initiators discover VD through NS queries.
    • The initiators always perform SCSI I/O operation to the virtual address of the VD.
    • At this point, either the initiator or target can be VD, but not both.
sdv manager contd
SDV Manager Contd..
  • SDV performs FCID translations on the frames destined to VD.
    • In the forward direction, DID is rewritten to that of the real target.
    • In the reverse direction, SID is rewritten to that of the VD.
  • The VD is hosted by one of the switches using a virtual domain.
  • The VD has an FCID and pWWN/nWWN assigned by the switch.
  • VD exists as long as its real counterpart is online. It inherits the FC-4 type and features from its real counterpart.
sdv solution the big picture
SDV Solution: The Big Picture
  • Configure a Virtual Target (VD) on MDS.
  • Initiator is zoned with VD.
  • VD is linked to a real (Primary) Target.
  • For control traffic (PLOGI, PRLI etc.)
    • MDS provides proxy functions. That is, it receives these ELS frames and re-transmits it to the real Target by performing NAT in header and payload.
  • For data traffic
    • MDS provides NAT of header VD FCID in hardware
  • The Primary and Secondary Targets can be on different MDS switches.
  • This features can be enabled on MDS without requiring a change on servers and storage arrays.
  • The admin can perform the Target Migration from primary to secondary through a single step configuration.





Virtual Target





Secondary Target

Primary Target

logical zones
Logical Zones
  • The {initiator, VD} is zoned. However the real target is not part
  • of any zone. Hence according to zoning the reverse path
  • frames from target to initiator would be dropped.
  • To overcome this restriction a logical zone is created with
  • {initiator, target} and Zone Server is notified.
  • The purpose of this logical zone is to make sure that w.r.t. the
  • targets it is zoned with the initiators, but w.r.t. the initiators
  • they are not zoned with the target.
  • The logical zone is not present physically in the active
  • ZoneSet. Hence presence of this zone not known to others.
  • Logical Zones known only to SDV switches. Hence solution is
  • limited to those devices that are directly connected to SDV
  • enabled switch.
solution step 1 creating the vd
Solution Step 1: Creating the VD






Virtual Target




  • A VD defined by user configuration enumerating all
  • the targets (primary and secondary)
  • When a VD is created
  • SDV picks a unique pwwn for the VD.
  • Registers the VD name with its pwwn as an Device Alias.

t1pwwn t1





solution step 2 zoning vd with initiators
Solution Step 2: Zoning VD with Initiators








Virtual Device

  • When VD name is zoned with initiators and activated …
  • SDV assigns FCID for VD.
  • SDV Registers VD with NS and sends SW-RSCN for VD once the primary target is online.
  • Inform ZS about presence of Logical Zone (dotted
  • in the diagram).

t1pwwn t1





solution step 3 linking vd with target
Solution Step 3: Linking VD with target








Virtual Device

  • When VD is linked with real target
  • ACL Rewrite entries are programmed to do the header NAT of data frames on access ports.
  • ACL Capture entries are programmed for payload NAT of Control frames (ELS) by the SUP.

t1pwwn t1





hosting the vd
Hosting the VD
  • Hosting involves injecting the virtual entities (VD) into
  • the fabric.
  • Hosting done by one switch; But it cannot use its local domain
  • for the VD FCID because if this switch leaves the fabric OR the
  • local domain changes, FCID would have to change.
  • The hosting switch reserves a Virtual Domain used for
  • assigning to VD. If the hosting switch goes down another
  • switch could take over its role using the same virtual domain.
  • Virtual Domain reservation to be used for the VD is through
  • Domain Manager using the RDI mechanism.
  • The route for virtual domain is advertised by hosting switch
  • through FSPF.
  • Hosting consists of: FCID allocation, NS registration,
  • SW-RSCN generation, Injecting Zones and route advertisement.
rewrite entries els capture entries
Rewrite Entries & ELS Capture entries
  • Rewrite entries are programmed in ACL TCAM for
  • FC header fcid-rewrite of the data traffic.
    • For each <initiator,target> pair two rewrite entries are needed. One in the
    • forward direction and one in the reverse direction.
    • Each ACL Rewrite entry includes zoning, forwarding and rewrite
    • information and avoids using FIB lookup/adjacency. The rewrite entry
    • would overwrite the zoning entry.
  • ELS capture entries are programmed for FC payload fcid
  • rewrite of the control traffic.
    • All the ELS frames to VD are punted to Supervisor.
    • The SDV module running on Sup does payload fcid-rewrite depending on
    • the ELS type and forwards it on the egress interface.
    • Some of the ACC frames also need payload fcid-rewrite.
frame translation with rewrite entries

i1 vt1

i1 t1

t1 i1

vt1 i1

Frame translation with rewrite entries



ACL entries

Frame values Rewrite values


i1 vt1 i1 t1

i2 vt1 i2 t1


t1 i1 vt1 i1

t1 i2 vt1 i2


t1pwwn t1

header and payload rewrites
Header and Payload rewrites

PLOGI trapped and punted to supervisor for payload FCID rewrite

Supervisor forwards frame to egress line card for header FCID rewrite

SCSI commands are forwarded to egress line card for FCID header rewrite


Device-Alias created with this name automatically

Real target PWWN

  • Enable the feature

(config)# sdv enable

  • Create a VD(config)# sdv virtual-device name disk vsan 1

(config-sdv-virt-dev)# pwwn 21:00:00:20:37:a9:d7:42 primary

  • Zone VD with desired devices

(config)# zone name zone1 vsan 1

(config-zone)# member pwwn <initiator> (config-zone)# member pwwn <VD-pwwn assigned by MDS>

  • Activate ZoneSet (regular zoneset activation)

(config)# zoneset activate name <zs> vsan <>

  • Link with current primary real target

(config-sdv-virt-dev)# link pwwn 21:00:00:20:37:a9:d7:42

  • (Use the same ‘link’ command to switch to secondary target if primary goes down)

(config-sdv-virt-dev)# link pwwn 22:00:00:20:37:a9:d7:42

Real initiator PWWN

PWWN assigned by MDS to represent target to host

Different pwwn that exposes same luns

domain fcid and pwwn used for vd
Domain, FCID, and PWWN used for VD

switch# show sdv virtual-device name disk

virtual-device name disk vsan 1

[ WWN:50:00:53:00:00:cd:c0:01 FCID:0x140654 Real-FCID:0x7c03e4 ]

pwwn 21:00:00:20:37:a9:d7:42 primary

FCID used to represent the real target

PWWN assigned by MDS.

Use this for zoning with real initiator

RTP9-CAE-POD2-9509# sh fcdomain domain-list


Number of domains: 2

Domain ID WWN

--------- -----------------------

0x64(100) 20:01:00:05:30:00:49:1f [Local] [Principal]

0x14(20) 50:00:53:07:ff:f0:00:71 [Virtual (SDM)]

Domain used to represent DID for the Virtual Devices hosted by this switch for this VSAN

locking down the domain and fcid used for the vd
Locking down the domain and FCID used for the VD
  • The hosting switch will reserve a DID for the VDs
  • It can not be the same DID assigned to the VSAN in the event that another switch has to assume the hosting of the VD.

switch(config-sdv-virt-dev)# ?

Configure a Virtual-device:

device-alias Add a device-alias to the Virtual-device

do EXEC command

end Exit from configure mode

exit Exit from this submode

link Link the Virtual-device to a real device

no Negate a command or set its defaults

pwwn Add a pwwn to the Virtual-device

virtual-domain Configure the persistent virtual domain

virtual-fcid Configure the persistent virtual fcid

Configured under virtual device

sdv enable

sdv virtual-device name disk1 vsan 1

virtual-domain 138

virtual-fcid 0x8a197f

pwwn 21:00:00:04:cf:17:66:b7 primary

sdv commit vsan 1



multi switch fabric
Multi-switch Fabric
  • SVD enabled on one of the switches that acts as the hosting switch. Eg: SW1 is the hosting switch
  • The frame rewrite has to happen only
  • on this hosting switch. Eg: Even though the traffic between I2 and T1 need not go thru SW1, it goes thru SW1 (because of VD’s fcid)
  • Drawback: Does not work if any switch
  • in path from initiator to target is not
  • SDV enabled. (logical zone unaware)
  • Other Drawbacks:
  • - The hosting switch is the single
  • point of failure.
  • - Hosting switch failure recovery
  • requires manual intervention.
  • - Non optimal routing of data frames.