KERNSAFE - iSCSI SAN Software and Storage Virtualization

Each time, only one user can update the iSCSI disk content. Two or more users writing the iSCSI disk synchronously is not allowed. This is because Windows system handles iSCSI device like handling a real hard drive. For disk operation, it is impossible to write the disk within two different computers.

Why can't two or more initiators write to the remote disk at the same time?

iSCSI really is just the handling of data blocks to and from the hard disk. Think of it as an extension of the hard disk that goes across the wire. If you have multiple servers connected to a volume it is exactly like having a shared SCSI bus between multiple hosts. There is nothing in the SCSI controllers to prevent you from corrupting your shared volumes. This kind of control needs to come from the operating system. The OS needs to know the volume is shared and either a special file-system or special handling needs to take place. Two or more clients connected to KernSafe iSCSI SAN(or other iSCSI Targets) with write access is supported. But it is in block mode, and most of the file systems in windows is not supported, doing this will result in files corruption.

When using iSCSI initiator to write iSCSI disk, the file updated might not be seen immediately at server. This is because of the system cache in the windows. But KernSafe iSCSI SAN has provided a feature called “Hold and Update”. This feature is based on file caching technology, targeting to reduce the network communication data and to achieve better performance.

Why does the iSCSI Initiator copy files in to remote disk can't be seen in the target?

Just like we can't use two or more initiators write the remote disk at the same time, because of the cache, the "Hold and Update" mechanism can help you do that.

To use hold and update mechanism, server machine(iSCSI Target) should have the following properties:

• No files is opened on target drive.
• No program in target drive is running.
• The target drive is a Disk Partition device.

Next, I will guide you to this work:

After KernSafe iSCSI SAN 1.27, there is a option in Create Target wizard and Device Settings that allow you to use the Hold and Update mechanism, see figure 1 and figure2.

Figure1

Figure 2

When the target with Hold and update support option is created, you can login with your CHAP user name and secret by using iSCSI Initiator to obtain Full Access. If you do not know how to do this, you can see the topic KernSafe iSCSI SAN Quick Start. Once the connection is established, this volume can't be used in the iSCSI Target machine, see Figure 3.

Figure 3

After you copied some files or done other operation for data files, and then logout from this KernSafe iSCSI SAN.

Ok, you will be able to open this volume and see the data files updated from initiators.