Flexible Data Storage Across Networks: iSCSI put to the Test

Possible Applications

iSCSI also lends itself to backup tasks, as information can easily be replicated to another drive, even if the target volume is in a neighboring building or another subsidiary connected through a broadband line. For example, this can be done using the volume shadow copy functionality built into Windows. iSCSI can even be operated over an ordinary DSL line, though here bandwidth may be the limiting factor, depending on the application.

The great advantage of iSCSI is that classical backups are now no longer limited to one location - an advantage that should not be underestimated. For example, devices such as tape libraries could be installed at any place in the company network. Even if a worst-case scenario does come to pass, the backup data that was saved via iSCSI can be replicated within a very short time frame.

Bearing The ISCSI Workload

If an iSCSI solution is implemented in software, the network adapter is hit by massive amounts of data. This workload is then delegated to the CPU courtesy of the NIC driver, since ordinary network adapters don't usually offer acceleration functions. SCSI is a block-oriented protocol, and Ethernet is packet-oriented. Due to the large amount of information that can be moved using Gigabit Ethernet, the embedding and extraction of blocks to and from TCP/IP packets can take up most or even all of the CPU cycles even on a modern system.

To ameliorate this problem, special TOEs (TCP/IP Offload Engines) were developed, which handle all of these complex operations right on the iSCSI network adapter. This takes the load off of the system's CPU, so the users and the server system can continue with their normal work.

Anyone planning to set up a high-performance iSCSI environment should either steer clear of software solutions or ensure a decent system environment. Adaptec offers a possible solution with its ASA-7211C and the Storage Array iSA 1500, which we will present on the following pages.

Create a new thread in the US Reviews comments forum about this subject
This thread is closed for comments
No comments yet
Comment from the forums
    Your comment