Alacritech - iSCSI FAQ

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iSCSI FAQ

Alacritech iSCSI Overview
Configuration
Troubleshooting
1. How do I troubleshoot iSCSI initiator problems?
2. I can't reconnect to my iSCSI session after reboot.

Alacritech iSCSI Overview

Q. What is the relationship between iSCSI and TOE (TCP Offload)?: Strictly speaking, iSCSI is just another TCP application and any software iSCSI initiator should work with any NIC, whether it employs TOE or not. It just happens that iSCSI is an application that benefits greatly from TCP offload.
Q. Is the Alacritech iSCSI Accelerator an iSCSI HBA (Host Bus Adapter)?: No. A true iSCSI HBA appears to the operating system as a hard disk controller. iSCSI HBAs offload all storage processing from the host. Alacritech iSCSI Accelerators appear to the operating system a a NIC. iSCSI Accelerators only offload the network packet processing, and require a software initiator to handle the translation of the storage request into the iSCSI protocol. In general, it is the TCP packet processing that places the greatest load on the host, so an iSCSI accelerator provides the same essential benefit as an iSCSI HBA.
Q. Does Alacritech provide a software iSCSI initiator?: Not at this time. We do maintain a list of supported initiators.
Q. Can I use the Alacritech iSCSI Accelerator as a regular NIC?: Yes, but it will only provide offload to iSCSI traffic. Other network traffic will not be offloaded. If you need to do offload of all your network traffic rather than just the iSCSI portion, you will need to use a TOE NIC (TNIC) such as an Alacritech Network Accelerator.
Q. Can I use the Alacritech iSCSI Accelerator with a Windows iSCSI target?: Absolutely! Because the Alacritech iSCSI Accelerator offloads any TCP traffic with a source or destination port of 3260, it will provide the same offload benefits on the target side as it provides on the initiator side. Note that proper operation of iSCSI targets with Alacritech Network or iSCSI Accelerators may require special configuration.
Alacritech maintains a list of tested software iSCSI targets.

Configuration

Q. Should I run regular network traffic on the iSCSI interface?

It is not recommended, as network resource contention will reduce iSCSI performance. Ideally, all iSCSI traffic should be separated from other network traffic by subnetting and by using VLANs or isolated physical LANs. A typical iSCSI connected server will have at least two network interfaces, one for regular LAN traffic on the LAN subnet, and second for iSCSI traffic on a private SAN subnet.

Note that many target vendors employ various types of in-band managment, which results in occaisional non-iSCSI traffic on the iSCSI subnet.

Q. Can I boot off of iSCSI disks?

Yes you can. All gigabit Alacritech Accelerators (Both SES and SEN products) except first generation products¹ support iSCSI boot. Alacritech support for iSCSI boot is currently via the netBoot/i and winBoot/i products from emBoot. Consult the iSCSI boot guide to learn how to use Alacritech Accelerators in an iSCSI boot environment.

1. First generation Alacritech gigabit products are: 2000-100007, 2000-100009, SES1001XT, and SES1001XF

Q. Can I run dynamic disks with the Microsoft initiator?

The Microsoft SCSI initiator user guide (v2.0) states categorically that they do not support dynamic disks. As far as we know, no other software initiator supports dynamic disks on windows either.

Q. Are disks larger than two terabytes supported?

Only on operating systems that support GPT (GUID Partition Table). See the Microsoft GPT FAQ for a list operating systems that support GPT.

When you first connect to a raw LUN that is larger than 2 TB with a GPT capable OS, the disk will show up in disk management as unknown/not initialized.

The disk signature wizard should pop up. If it doesn't, just right click on the disk and select initialize. The wizard will split the disk into a bunch of 2TB MBR partitions, which is probably not what you want.

Right click on the disk and select Convert to GPT. The end result should look something like this:

You can now create a new partition in the normal fashion and end up with a partition greater than two terabytes.

Remember, this partition will only be accessable to hosts that support GPT.

Q. When using the Microsoft initiator, how do I get shares on an iSCSI disk to come back after reboot?

This is usually only an issue if you are using the Microsoft iSCSI initiator version 1.06 or earlier. As of release 2.0, Microsoft has placed msiscsi into a load order group. If your target is supported with the 2.0 MS iSCSI intiator, then you should upgrade.

If you must use the 1.06 initiator, then use one of the following two procedures:

Method 1:

Make sure your disks are persistent and set up to autologin.
Make sure that you bind your iSCSI disks.

Make the Server service depend on the MSiSCSI service.

Check the registry key:
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Lanmanserver
If it's not already there, add the following value:

Value Name		DependOnService
Data Type		REG_MULTI_SZ
Range		Service Name(s)
Default Value		none
Recommended Value		MSiSCSI

Method 2:

If you mount your iSCSI drives onto NTFS partitions, i.e. on junctions, rather than as drive letters, it is not necessary to make the Server service depend on the MSiSCSI service

Q. What configuration changes do I need to make for use with iSCSI target software?

Applies to: Non-SNP aware drivers only.
To increase performance, Alacritech ignores the push flag by default on well framed protocols such as CIFS and iSCSI. Certain Windows-based iSCSI target software, including products from Rocket Division and Stringbean Software (wintarget) will hang waiting for data if the push flag is ignored. Other targets that operate in kernel space rather than user space, such as Falconstor IPStor, function correctly when the push flag is ignored. A new registry setting is available to change push flag processing for iSCSI. Changes to this parameter are not required for proper operation of the Microsoft iSCSI Software Initiator.

Using Regedit, add a new parameter to:
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ATCP\Parameters

Value Name		IgnorePushPort3260
Data Type		REG_DWORD
Range		0 or 1
Default Value		1
Recommended Value		Change to 0 when using user space iSCSI target software.

Description: This key determines whether the push flag is ignored for iSCSI traffic on port 3260. If IgnorePush3260 does not exist or if it is set to 1, the push flag will be ignored on port 3260. Set the value to 0 to obey the push flag for use with user space iSCSI targets.

You must reboot the host for this change to take effect.

Q. Are there performance tuning changes I should make for iSCSI?

There are some changes that can be made that may improve iSCSI connectivity and performance:

First, disable NetBT on the iSCSI network interface.: WARNING: If you disable NetBT on the iSCSI network interface, you should also disable NetBT on the iSCSI network interface of all other hosts in your environment. If you fail to do this, services that depend on NetBT, such as Windows file sharing, may fail to function.
Next, under the Advanced tab in the Network Connections window, select Advanced Settings.
Set the interface order such that the iSCSI interface is listed first and disable all bindings to the iSCSI interface.
Finally, under Provider Order, move Microsoft Windows Network to teh top of the list.

Q. How do I decide between teaming or MPIO?

It depends on what you are trying to accomplish.

In environments where pure single stream performance is the overriding criterion MPIO is the preferred option. MPIO has the ability to distribute a single stream across multiple ports thus maximizing data throughput. In environments where high availability is the main concern, then teaming is preferred, as failover occurs much more quickly. Also, many targets do not support Active-Active operation, and thus cannot use MPIO modes that enhance single stream performance.

The full answer is a bit too complicated to fit into this FAQ. We're working on a guidelines page. When it is ready, there will be a link to it from this question.

Q. Can I use the iSCSI interface for cluster traffic an an MS iSCSI cluster?

No. The iSCSI network should be completely excluded from use for cluster network traffic. See the question titled "Are there any iSCSI-specific requirements?" in the Microsoft iSCSI Cluster Support FAQ.

Here is an example of what we mean using a single node cluster:

In this example, the 10.1.0.0 subnet is the private network (In production, we wouldn't have a default gateway on this subnet, and we'd disable NetBT as well). The 172.16.48.0 subnet is the public network. The 192.168.48.0 subnet it for iSCSI traffic. The host used in this example was configured to use MPIO, which is why there are two interfaces on the iSCSI subnet.

The ipconfig /all looks like this:

Windows IP Configuration

   Host Name . . . . . . . . . . . . : mayhem
   Primary Dns Suffix  . . . . . . . : csl.alacritech.com
   Node Type . . . . . . . . . . . . : Unknown
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : csl.alacritech.com
                                       alacritech.com

Ethernet adapter BCM1:

   Connection-specific DNS Suffix  . : 
   Description . . . . . . . . . . . : Broadcom NetXtreme Gigabit Ethernet
   Physical Address. . . . . . . . . : 00-E0-81-2A-D1-A2
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 10.1.50.85
   Subnet Mask . . . . . . . . . . . : 255.255.0.0
   Default Gateway . . . . . . . . . : 10.1.1.1

Ethernet adapter SES_A:

   Connection-specific DNS Suffix  . : 
   Description . . . . . . . . . . . : Alacritech SES2002XT iSCSI Accelerator Slot #3 Port A
   Physical Address. . . . . . . . . : 00-10-42-00-B7-3C
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 192.168.50.85
   Subnet Mask . . . . . . . . . . . : 255.255.252.0
   Default Gateway . . . . . . . . . : 
   NetBIOS over Tcpip. . . . . . . . : Disabled

Ethernet adapter SEN_A_csl:

   Connection-specific DNS Suffix  . : 
   Description . . . . . . . . . . . : Alacritech SEN2002XT Accelerator Slot #1 Port A
   Physical Address. . . . . . . . . : 00-10-42-00-B9-FE
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 172.16.51.80
   Subnet Mask . . . . . . . . . . . : 255.255.252.0
   IP Address. . . . . . . . . . . . : 172.16.50.85
   Subnet Mask . . . . . . . . . . . : 255.255.252.0
   Default Gateway . . . . . . . . . : 
   DNS Servers . . . . . . . . . . . : 172.16.50.1
                                       172.16.50.2

Ethernet adapter SES_B:

   Connection-specific DNS Suffix  . : 
   Description . . . . . . . . . . . : Alacritech SES2002XT iSCSI Accelerator Slot #3 Port B
   Physical Address. . . . . . . . . : 00-10-42-00-B7-3D
   DHCP Enabled. . . . . . . . . . . : No
   IP Address. . . . . . . . . . . . : 192.168.50.105
   Subnet Mask . . . . . . . . . . . : 255.255.252.0
   Default Gateway . . . . . . . . . : 
   NetBIOS over Tcpip. . . . . . . . : Disabled

Before setting up the cluster, we configured and tested the iSCSI and MPIO, but that process will not be detailed here.

When the cluster configuration wizard finished, it had attached to one interface on each subnet.

Cluster Network Resources

Cluster Network Interface Resources

This is not correct, the iSCSI network must be excluded from cluster use. We select the properties of SES_A under cluster networks and uncheck the box that allows the cluster to use this network.

Properties Pane of the SES_A Cluster Network Resource

We don't need to do anything with the SES_A cluster network interface resource, once the network is excluded, all interfaces on that subnet will be excluded as well.

Afterwards, it looks like this:

Cluster Network Resources

Cluster Network Interface Resources

Troubleshooting

Q. How do I troubleshoot iSCSI initiator problems?

Start by verifying you configuration. The majority of iSCSI support calls handled by Alacritech are simply due to incorrect configuration.
Next, test the underlying network as outlined in our Accelerator FAQ troubleshooting section.
Next, disable TCP offload on the iSCSI Accelerator. If the problem still occurs, then it is probably an issue with your iSCSI configuration. The convrse of that is that if the problem does go away with offload disabled, you should Contact Alacritech Support

Q. I can't reconnect to my iSCSI session after reboot.

The workarounds outlined here may help.