Sign in with
Sign up | Sign in
iSCSI The Open-E Way
By ,
1. Instant iSCSI By Open-E

Open-E's iSCSI product can be called "iSCSI-on-a-chip," as it integrates an UltraATA interface with the integrated Linux-based software that is stored on a flash memory component.

Storage companies have maintained the same thing now for almost three years: Direct attached storage (DAS) is inflexible and creates bottlenecks, while its administration is time consuming. The future of professional storage, they say, belongs to networked appliances that allow placing storage units anywhere within your network. Switching to iSCSI will thus take storage to the next level, they say.

So if iSCSI really is that good, why has it not taken off yet? In addition to the high price of Fibre Channel infrastructures that are required for high-performance applications, technical barriers remain. A look at iSCSI in detail and its evolution accounts for the protocol's limited adoption.

iSCSI is a shortcut for Internet SCSI, in which SCSI stands for the small computer system interface that is the predominant DAS storage interface in the professional space.

The iSCSI protocol is used to encapsulate native storage data into IP packages, which in turn allows for transferring this data over existing networks as if these were a local storage interface such as UltraSCSI. Due to the large variety of IP networks (PAN, WLAN, LAN by means of Ethernet or Fibre Channel, WAN, MAN and the Internet), a storage area network (SAN) based on the iSCSI protocol can technically bridge any distance, and it is only limited by the performance of the particular network(s) it uses.

Knowing this, it becomes obvious that a SAN is typically kept within the limits of a fast network neighborhood, which brings us back to the barriers we mentioned: Storage devices that respond to multiple client requests require adequate bandwidth to do so. A 100 Mbit Ethernet network, for example, is technically capable of hosting iSCSI, but its performance would not really be up to task. Fibre channel, on the opposite end of the spectrum, often is too expensive for small- and medium-sized businesses.

The rapid deployment of gigabit Ethernet (GbE), however, gradually creates a substantial backbone for iSCSI applications. Although GbE over fiber cable is the state-of-the-art solution, we estimate that GbE over copper wire networks will further accelerate the transition from direct attached storage to storage area network applications; this type of infrastructure is also backwards compatibility and is available at an attractive price point.

2. Between Fibre Channel And Ethernet

The concept behind iSCSI arose from traditional storage interfaces such as ATA or SCSI being limited to a single machine and a maximum cable length. Flexibility of business and enterprise class storage applications hence is rather limited. So, ideally, storage should be detached from particular servers in order to increase flexibility and to avoid bottlenecks. In the end, administrators should be able to add, move, backup, restore or reconfigure storage without having to change running systems or look after multiple servers. Swapping out storage by using existing network infrastructure thus seems to be a good approach.

It is easy to spend several hundred dollars for SCSI cables or, even worse, a lot of money for Fibre Channel cabling and accessories. Fibre channel became the premier interface for professional applications and SANs because of its high throughput and long operating range. Fibre channel connections can be up to 30 meters in length when twisted pair copper cables are used, or up to 10 kilometers when based on a fiber optics link, with data transfer rates of 2 Gb/s or 4 Gb/s. Fibre channel is thus capable of connecting systems throughout a huge corporate campus for which very high data transfer rates and maximum performance are required.

In addition, Fibre Channel can point-to-point-connect two devices, be set up using switches or be operated in an arbitrated loop similar to Token Ring. Apart from that, it can carry ATM cells, IP packages or SCSI commands by fitting these into its own frames (which are not compatible with Ethernet). For these reasons, Fibre Channel is dominant in the enterprise space.

Fibre Channel storage components are considered the only choice for high-end environments such as data processing or huge database applications. The infrastructure can be used as an interface between hard drives and host bus adapters, or for linking systems and/or storage units within a SAN - or both. However, as soon as an enterprise does not require data to be locally available at a maximum speed, the extra costs do not make sense: Why not opt instead for storage subsystems based on Serial ATA components, and use the existing Gigabit Ethernet infrastructure?

3. Storage Is No Different Than Printing

The direction that professional storage has taken is similar to that of printers. Previously, at home, we connected printers directly to our computers via a parallel or USB port. In corporations, they were positioned in places where it physically made the most sense. Printers, for example, could be found next to employees that had to print frequently, or attached to computers dedicated only for printing.

Then, the introduction of printers with network interfaces such as HP's LaserJets with the JetDirect interface option allowed for a more flexible positioning and administration. Printers became independent from their host computers.

Storage is headed in the same direction. Now, most users install more hard drives when they run out of capacity. However, concerns about where data is stored, available capacity or whether a file server is down or not can be less of an issue.

Indeed, even small businesses should consider moving away from the concept of operating file servers in favor of network attached storage (NAS) devices or flexible storage systems within a storage area network (SAN). These networked storage applications allow for increased flexibility, scalability, availability; backup options are increased and where the storage server is physically located is much less of an issue.

iSCSI Targets And Initiators

iSCSI accommodates a server and multiple clients. The server is called a target and typically is either a dedicated storage computer, or a server that has access to direct attached storage. The storage management software can be part of the storage system (this is the case with Open-E's iSCSI) or is simply installed onto a host system. We used DataCore's SANmelody iSCSI target software to review the Open-E iSCSI system.

The clients are called iSCSI initiators. Provided that you have a user account that has access to the desired iSCSI target, you can simply use the Microsoft iSCSI Initiator: it can be downloaded on Microsoft's Website and is free of charge. It uses CHAP (Challenge Handshake Authentication Protocol) to log onto an iSCSI target. Simply provide the iSCSI target IP and your login data, and you are ready to go. After login, the iSCSI target will appear as a system drive to Windows, because the iSCSI initiator behaves as if it were a storage adapter (which it effectively is). Although the iSCSI target may be far away, you have the same access as you would with a local hard drive.

4. Open-E iSCSI Enterprise 1.51 In Detail

Maybe you still remember the NAS modules that Open-E has been offering since the beginning of 2004. These are specialized Linux systems stored on a flash memory module that is attached to the system via UltraATA. After plugging the Open-E NAS module into a bootable UltraATA port, the system will boot the highly customized operating system that turns the host system into a powerful and flexible NAS server. The hardware configuration depends on your requirements and supports anything from a single hard drive up to multiple RAID controllers (Enterprise edition only). Anything else can be configured using a Web browser.

It's not hard to guess that Open-E took its system core and made some modifications. Open-E iSCSI is installed the same way and works on an equally large amount of host systems, but turns the host system into an iSCSI target rather than a NAS server. One huge advantage of Open-E's solution is that it comes with its own system 'drive' and operating system. You won't have to buy either one of these or can use existing resources for another purpose.

The beautiful thing about this solution is that the customer can add new features to the iSCSI storage system (or the NAS server) by simply updating the Open-E software as new versions become available. Yet, installing updates did not work as smoothly as we expected: After finishing the product registration (which is required), we were not able to run the update on a Gigabyte GA-955X Royal motherboard. The update program was unable to unpack the kernel. We had to switch to a MSI K8N Diamond Plus before we could successfully install the update.

However, since most users would not run a high-end storage system on a consumer type motherboard, we decided do use an Asus MT4, which is a Socket 775 server type motherboard with PCI-X slots, integrated graphics and twin Gigabit Ethernet ports. We picked AMCC's 9550SX SATA II RAID controller (it is on Open-E's compatibility list) and decided to set up a RAID 0 consisting of four Seagate NL35 drives (400 GB each). Though RAID 0 certainly is not what an administrator would choose, we figured that it might be the best way to prevent a storage subsystem bottleneck.

You have to enter the default password after booting the system. Open-E supports English and German since the company is based in Germany. Open-E iSCSI can be accessed from anywhere in the network via secured http using your Web browser.

5. System Setup


Open-E iSCSI is largely based on Open-E NAS, which is why we were not surprised to see support for Snapshots, Fibre Channel adapters and multiple network cards. The latter can be used to provide more bandwidth than what you would get using one network connection via iSCSI's multi-path feature. It is supported by Microsoft's iSCSI Initiator, but not necessarily by all software solutions that are available. However, you can still use multiple cards to share one iSCSI target between different subnets or between physically different networks.

System Status

6. Target Configuration

You may recall that we have a powerful SATA RAID controller and four drives that are ready to be used. All important settings, including the physical array creation, can be done using the nicely structured Web-based interface. The only action that requires the user to perform locally is the deletion of RAID arrays. For security reasons this can only be done using the RAID controller's local interface. We used this interface to create one large RAID 0 array prior to booting the Open-E iSCSI. At this point we should mention that the latest Open-E iSCSI version 1.51 also supports host system based RAID, which allows for the integration of several drives with one another in order to set up a RAID 0, 1, 0+1 or RAID 5 array.

Our four 400 GB hard drives result in a total net capacity of 1,490 GB, because one of these drives features 372 rather than 400 GB in reality. A kiloByte represents in reality 1,024 Bytes and not 1,000 Bytes, according to the definition of the storage industry.

The slider (see screenshot above) can be used to select the size for your iSCSI target. You can also opt to create a snapshot space, which can be used to backup the state of a target volume.

The next step in creating an iSCSI target is to provide a target name and access data.

Don't forget the checkbox to enable the login access control that you just defined. As an additional security feature, it is possible to restrict access to certain IP addresses only.
7. Datacore SAnmelody 2.0

SANmelody can be integrated with Microsoft's Storage Management console.

SANmelody has been around longer than Open-E's iSCSI and certainly is the more sophisticated iSCSI solution. However, it requires a fully functional host system, which includes a system hard drive and an operating system license. In addition, SANmelody's price starts at around $1,178 and thus doubles the costs for the Open-E iSCSI Enterprise edition. Yet you can spend another $864 on an upgrade option that will provide the snapshot feature and auto provisioning, which takes care of allocating the available capacity dynamically rather than assigning fixed segments per iSCSI target. This, we have to say, is indeed pretty nice. However, multi teraByte and multi processor support again has to be purchased separately.

With the exception of the entry-level version, SANmelody supports Fibre Channel and offers some features that Open-E still cannot compete with: You may define auto failovers and go for asynchronous IP replication (this you will need for replicating data over the Internet), which allows for the creation of high-availability storage solutions based on mirrored systems. This, obviously, caters to the area of mission critical applications. See this page for all available versions. Should SANmelody not be capable of answering to your requirements, SANsymphony likely can, because it's the company's offering for 'large scale storage consolidation and automation.'

One downside is the more complex interface: While we believe that even a beginner can set up Open-E iSCSI, you should have a certain degree of experience before playing around with SANmelody.


DataCore is both very scalable and costly.


SANmelody Storage Servers will appear as devices within the storage management section of Microsoft's Management Console.


It will display all available volumes.
8. Create Virtual Drives


Virtual drives need to be created in order to provide storage to iSCSI initiators (clients).


Network channels must be assigned prior to access storage volumes. If multiple network adapters are available, these can all be selected if you want to enable multiple lanes.


Finally, the available channels must be linked to virtual volumes.
9. Microsoft's iSCSI Initiator

Each iSCSI initiator carries a name (initiator node) and certain settings regarding authentication (via CHAP) and link security (IPsec).

Provide your iSCSI target here. iSNS servers (Internet Storage Name Service) help in the discovery of iSCSI targets unless these are invisible to the network. However, iSNS is only interesting for larger scale applications.

Of course it is possible to log onto multiple iSCSI targets at a time. This can be done using a single network connection, or via separate network cards. We would recommend routing high-performance iSCSI applications over dedicated network branches, which helps to keep performance at the highest possible level.

Note the local adapter choice: Here you may select iSCSI Accelerator cards instead of the Microsoft client. The CHAP logon requires username and password to logon to iSCSI targets.


We selected a rather small capacity when configuring our test target, since it would finish the benchmarks quicker than large storage spaces.
10. Test Setup
System Hardware I (for DataCore SANmelody 2.0)
Processor(s) 2x Intel Xeon Processor (Nocona core)
3.6 GHz, FSB800, 1 MB L2 Cache
Platform Asus NCL-DS (Socket 604)
Intel E7520 Chipset, BIOS 1005
RAM Corsair CM72DD512AR-400 (DDR2-400 ECC, reg.)
2x 512 MB, CL3-3-3-10 Timings
System Hard Drive Western Digital Caviar WD1200JB
120 GB, 7,200 rpm, 8 MB Cache, UltraATA/100
Mass Storage Controller(s) Intel 82801EB UltraATA/100 Controller (ICH5)
Adaptec AIC-7902 Ultra320
Networking Broadcom BCM5721 On-Board Gigabit Ethernet NIC
Graphics Card On-Board Graphics
ATI RageXL, 8 MB
System Hardware II (for Open-E iSCSI Enterprise 1.51)
Processor(s) Intel Pentium4 560 Processor (Prescott core)
3.6 GHz, FSB800, 1 MB L2 Cache
Platform Asus P5MT (Socket 775) Rev. 1.04
Intel E7230 Chipset, BIOS 1001
RAM Corsair CM2X512A-5400UL (XMS5400 V1.2)
2x 512 MB - DDR2-667 (266 MHz, CL4)
System Hard Drive Samsung SpinPoint P120 P620JJ
120 GB, 7,200 rpm, 8 MB Cache, SATA/300
Mass Storage Controller(s) Intel 82801UltraATA/100 Controller (ICH7R)
AMCC 3Ware 9550SX
Networking Broadcom BCM5721 PCI-E Gb LAN
Graphics Card On-Board Graphics
ATI RageXL, 8 MB
System Hardware
Performance Measurements c’t h2benchw 3.6
I/O Performance IOMeter 2003.05.10
Fileserver-Benchmark
Webserver-Benchmark
Database-Benchmark
Workstation-Benchmark
System Software & Drivers
OS Microsoft Windows Server 2003 Standard Edition, Service Pack 1
Platform Driver Intel Matrix Storage Manager 5.1.0.1022
Graphics Driver Default Windows Graphics Driver

Seagate NL35 Drives

11. Benchmark Results

Data Transfer Diagrams

Open-E iSCSI Enterprise Edition 1.51

Open-E's iSCSI Enterprise does not seem to be limited when it comes to data transfer performance. Almost 90 MB/s is close to the net maximum that a Gigabit Ethernet is capable of transferring using iSCSI.

DataCore SAnmelody 2.0

The data transfer performance of the DataCore SANmelody solution seems to be somewhat limited, as it does not exceed 70 MB/s.

12. Access Time

Here, Open-E's iSCSI Enterprise clearly provides the better results. Average access times of 8.1 ms versus 10.2 ms make quite a difference. At this point, you may wonder how such a quick access time is possible, as the 7,200 RPM drives that we are using perform in the area of 12-14 ms. It is the iSCSI solutions' cache algorithms that allow for shortening access times here. While this can sometimes be an advantage, it certainly does not reflect the real average access time of the iSCSI target.

Bandwidth

These results basically reflect the maximum bandwidth between the iSCSI target and our initiator system. As you can see, the bandwidth hits the limits of Gigabit Ethernet with Open-E iSCSI Enterprise (125 MB/s).

13. Transfer Performance

Open-E's data transfer performance is clearly superior, although the DataCore solution is capable of sustaining a much better minimum transfer rate.

14. PCMark05 Windows Startup Performance

Although we have not seen a solution that would allow booting a system via an iSCSI drive, we still decided to include this benchmark. With this application-based benchmark, there is not much of a difference between DataCore and Open-E. Open-E has a very small lead here.

PCMark05 File Write Performance

Again, Open-E outperforms its competitor by a very small margin.

15. I/O Performance

If you intend to run access-sensitive applications across an iSCSI infrastructure, the SANmelody by DataCore clearly is the superior solution. Depending on the command queue depth, it is capable of handling 15-100% more I/O operations per second and beats the pants off of Open-E's iSCSI Enterprise edition.

16. Conclusion

While DataCore has been in the iSCSI arena since 1998 (longer than Open-E), both solutions make a very good impression. SANmelody by DataCore is a full-fledged software solution for Windows Server. It is scalable, feature rich and impressively powerful, but costs a fortune if you need more than the basic package. At the same time it should be underlined that SANmelody was intended for enterprise customers.

Open-E's iSCSI modules come with their own system software, which means they have to compete with SANmelody's Windows-based Storage Services features and the massive worldwide driver support that Microsoft enjoys. However, an Open-E iSCSI can turn virtually any computer into a comprehensive iSCSI storage solution without requiring a Windows license, expensive hardware or complicated administration.

While it is the top version of the product family, Open-E's iSCSI Enterprise is only half the price of the basic SANmelody kit. The latter is clearly more sophisticated, but Open-E provides a better price-per-performance ratio for small- to medium-sized enterprises. Proof can also be found in the benchmark results: Open-E iSCSI dominates all disciplines except in I/O performance.

17. Feature Table
  DataCore SANmelody 2.0 Open-E iSCSI Enterprise 1.51
Solution Software solution. Requires Windows XP or Windows Server and .net Framework Linux based software on a Flash storage module, using UltraATA/100
Application Dedicated or shared storage server Dedicated storage server
Infrastructure Ethernet, Fibre Channel Ethernet, Fibre Channel
iSCSI Accelerator support, 10 GbE support All hardware with Windows drivers Chelsio 10 GbE
RAID support All RAID hardware with Windows drivers, Windows software RAID Most cards from AMCC/3Ware, Adaptec, ICP Vortex, Intel, LSI Logic. Software RAID support.
Network card support All hardware with Windows drivers Multiple cards
Fibre Channel HBA support All hardware with Windows drivers Emulex, Qlogic
Multilane support / load balancing Microsoft Multipath I/O yes
Data security features IPsec, Secure LUN allocation, iSCSI CHAP, asynchronous IP replication IPsec, iSCSI target passwords, iSCSI CHAP
Fault tolerance Auto failover option based on SANmelody disk servers Secondary HBA takeover
Snapshot support Complete image, image update, source update. Can be triggered by Windows Volume Shadow Copy Complete image with scheduling
Storage volume features Based on Windows Server 2003 Storage Services. Virtual Disks, Volume Shadow Copies, Multipath I/O Auto provisioning (dynamic allocation of storage) Multiple volume grouping, online volume expansion
Performance features I/O read and write caching using system RAM no information found
Administration Microsoft Management Console, rights controlled by OS SSL web interface, multiple access levels
UPS support yes, based on OS and UPS Yes, with SNMP network shutdown
Email notification yes yes
Logging yes yes
Multi processor support 1, 2, or 4 (depending on software package) up to eight logical processors
Hardware Requirements x86 PC, 300+ MHz, 512 MB RAM, 65 MB disk space, network card x86 PC, 1.4+ GHz recommended, 512 MB RAM, RAID controller recommended, network card
Software Requirements Windows XP Home/Pro or Windows Server 2003 with .net Framework None