iSCSI Target Server Scalability Limits

 

Updated: December 15, 2015

Applies To: Windows Server 2012, Windows Server 2012 R2

This topic provides the supported and tested Microsoft iSCSI Target Server limits on Windows Server 2012 R2 and Windows Server 2012. The following tables display the tested support limits and, where applicable, whether the limits are enforced.

General limits

Item

Support Limit

Enforced?

Comment

iSCSI target instances per iSCSI Target Server

256

No

iSCSI logical units (LUs) or virtual disks per iSCSI Target Server

512

No

Testing configurations included: 8 LUs per target instance with an average over 64 targets, and 256 target instances with one LU per target.

iSCSI LUs or virtual disks per iSCSI target instance

256 (128 on Windows Server 2012)

Yes

Sessions that can simultaneously connect to an iSCSI target instance

544 (512 on Windows Server 2012)

Yes

Snapshots per LU

512

Yes

There is a limit of 512 snapshots per independent iSCSI application volume.

Locally mounted virtual disks or snapshots per storage appliance

32

Yes

Locally mounted virtual disks don't offer any iSCSI-specific functionality, and are deprecated - for more info, see Features Removed or Deprecated in Windows Server 2012 R2.

Fault Tolerance limits

Item

Support Limit

Enforced?

Comment

Failover cluster nodes

8 (5 on Windows Server 2012)

No

Multiple active cluster nodes

Supported

 

N/A

Each active node in the failover cluster owns a different iSCSI Target Server clustered instance with other nodes acting as possible owner nodes.

Error recovery level (ERL)

0

Yes

Connections per session

1

Yes

Sessions that can simultaneously connect to an iSCSI target instance

544 (512 on Windows Server 2012)

No

Multipath Input/Output (MPIO)

Supported

N/A

MPIO paths

4

No

Converting a stand-alone iSCSI Target Server to a clustered iSCSI Target Server or vice versa

Not supported

No

The iSCSI Target instance and virtual disk configuration data, including snapshot metadata, is lost during conversion.

Network limits

Item

Support Limit

Enforced?

Comment

Maximum number of active network adapters

8

No

Applies to network adapters that are dedicated to iSCSI traffic, rather than the total number of network adapters in the appliance.

Portal (IP addresses) supported

64

Yes

Network port speed

1Gbps, 10 Gbps, 40Gbps, 56 Gbps (Windows Server 2012 R2 only)

No

IPv4

Supported

N/A

IPv6

Supported

N/A

TCP offload

Supported

N/A

Leverage Large Send (segmentation), checksum, interrupt moderation, and RSS offload

iSCSI offload

Not supported

              

N/A

Jumbo frames

Supported

N/A

IPSec

Supported

N/A

CRC offload

Supported

N/A

iSCSI virtual disk limits

Item

Support limit

Enforced?

Comment

From an iSCSI initiator converting the virtual disk from a basic disk to a dynamic disk 

Yes

No

Virtual hard disk format

.vhdx (Windows Server 2012 R2 only)

.vhd

VHD minimum format size

.vhdx: 3 MB

.vhd: 8 MB

Yes

Applies to all supported VHD types: parent, differencing, and fixed.

Parent VHD max size

.vhdx: 64 TB

.vhd: 2 TB

Yes

Fixed VHD max size

.vhdx: 64 TB

.vhd: 16 TB

Yes

Differencing VHD max size

.vhdx: 64 TB

.vhd: 2 TB

Yes

VHD fixed format

Supported

No

VHD differencing format

Supported

No

Snapshots cannot be taken of differencing VHD-based iSCSI virtual disks.

Number of differencing VHDs per parent VHD

256

No (Yes on Windows Server 2012)

Two levels of depth (grandchildren .vhdx files) is the maximum for .vhdx files; one level of depth (child .vhd files) is the maximum for .vhd files.

VHD dynamic format

.vhdx: Yes

.vhd: Yes (No on Windows Server 2012)

Yes

Unmap isn't supported.

exFAT/FAT32/FAT (hosting volume of the VHD)

Not supported

Yes

CSV v2

Not supported

Yes

ReFS

Supported

N/A

NTFS

Supported

N/A

Non-Microsoft CFS

Not supported

Yes

Thin provisioning

No

N/A

Dynamic VHDs are supported, but Unmap isn't supported.

Logical Unit shrink

Yes (Windows Server 2012 R2 only)

N/A

Use Resize-iSCSIVirtualDisk to shrink a LUN.

Logical Unit cloning

Not supported

N/A

You can rapidly clone disk data by using differencing VHDs.

Snapshot limits

Item

Support limit

Comment

Snapshot create

Supported

Snapshot restore

Supported

Writable snapshots

Not supported

Snapshot – convert to full

Not supported

Snapshot – online rollback

Not supported

Snapshot – convert to writable

Not supported

Snapshot - redirection

Not supported

Snapshot - pinning

Not supported

Local mount

Supported

Locally mounted iSCSI virtual disks are deprecated - for more info, see Features Removed or Deprecated in Windows Server 2012 R2. Dynamic disk snapshots cannot be locally mounted.

iSCSI Target Server manageability and backup

If you want to create volume shadow copies (VSS open-file snapshots) of data on iSCSI virtual disks from an application server, or you want to manage iSCSI virtual disks with an older app (such as the Diskraid command) that requires a Virtual Disk Service (VDS) hardware provider, install the iSCSI Target Storage Provider on the server from which you want to take a snapshot or use a VDS management app.

The iSCSI Target Storage Provider is a role service in Windows Server 2012 R2 and Windows Server 2012; you can also download and install iSCSI Target Storage Providers (VDS/VSS) for down-level application servers on the following operating systems as long as the iSCSI Target Server is running on Windows Server 2012:

  • Windows Storage Server 2008 R2

  • Windows Server 2008 R2

  • Windows HPC Server 2008 R2

  • Windows HPC Server 2008

Note that if the iSCSI Target Server is hosted by a server running Windows Server 2012 R2 and you want to use VSS or VDS from a remote server, the remote server has to also run Windows Server 2012 R2 and have the iSCSI Target Storage Provider role service installed. Also note that on all versions of Windows you should install only one version of the iSCSI Target Storage Provider role service.

For more info about the iSCSI Target Storage Provider, see iSCSI Target Storage (VDS/VSS) Provider.

Tested compatibility with iSCSI initiators

We've tested the iSCSI Target Server software with the following iSCSI initiators:

Initiator

Windows Server 2012 R2

Windows Server 2012

Comments

Windows Server 2012 R2

Validated

Windows Server 2012, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

Validated

Validated

VMWare vSphere 5

Validated

VMWare ESXi 5.0

Validated

VMWare ESX 4.1

Validated

CentOS 6.x

Validated

Must log out a session and log back in to detect a resized virtual disk.

Red Hat Enterprise Linux 6

Validated

RedHat Enterprise Linux 5 and 5

Validated

Validated

SUSE Linux Enterprise Server 10

Validated

Oracle Solaris 11.x

Validated

We've also tested the following iSCSI initiators performing a diskless boot from virtual disks hosted by iSCSI Target Server:

  • Windows Server 2012 R2

  • Windows Server 2012

  • PCIe NIC with iPXE

  • CD or USB disk with iPXE

The following list provides additional resources about iSCSI Target Server and related technologies.

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