Product Reviews

Fibre Channel may be the network infrastructure of choice for storage area networks (SANs), but the high cost of installation and management keeps them firmly in the enterprise sector. iSCSI (Internet SCSI) is designed to offer an alternative for medium-sized businesses that like the appeal of a SAN but have traditionally relied on lower-cost DAS and NAS solutions. The simplicity of iSCSI is a key factor in its favour, as it merely takes SCSI data blocks and maps them into Ethernet packets. Consequently, iSCSI can be implemented over standard Ethernet networks without the need for costly Fibre Channel equipment and cabling.

Overland Storage claims that the REO family of appliances is the very first series of iSCSI storage products to market and specifically targets data backup and restore acceleration. These are installed either between tape devices and backup servers or in between an application and backup servers. Data can be secured to the appliance from multiple servers simultaneously, and this can then be accessed by the backup server and secured to tape more efficiently. With eight disks supported in the R2000 and RA2000 (reviewed here), you can secure up to eight servers at the same time. The optional RX2000 disk array allows storage to be easily expanded as required.

The system comes with a good hardware specification. The iSCSI target services are handled by a Red Hat Linux kernel running on a Flash memory card. SATA (Serial ATA) is the storage medium of choice and a full 2TB is provided by eight 250GB Western Digital Caviar hard disks. The drives are managed by a 3Ware Escalade eight-port SATA controller but hardware RAID isn't supported. Naturally, once you've logged multiple drives into an iSCSI initiator you can create software-based RAID-0, -1 or -5 arrays; the drives aren't hot-swappable and the chassis must be powered down before they're removed. Management access is provided with a single 10/100BaseTX port at the front on the chassis, while data is accessed via a pair of 1000BaseT ports on the other side.

Installation is fairly straightforward, although the documentation fails to mention that the management port and data ports must not be on the same subnet. If they are, a conflict

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will cause the data ports to become unavailable. Network setup starts by inserting the supplied USB keyring drive into a workstation and editing the configuration file for the management Ethernet port. All you add here are basic network details, after which the drive can be plugged into the rear of the REO where the information is used to start the appliance. The key also appears as a network drive which can be mapped and used to download software upgrades. The appliance supports browser management and the main interface is very simple due to the limited number of options. From the System menu each data port can be assigned an IP address. A new workgroup name or a domain can be provided for the appliance to join and a couple of email addresses can be entered for alert forwarding. From the iSCSI menu you can select each drive, assign multiple target names and view their status and that's about all. The USB drive also provides a pointer to Microsoft's website where you can download the iSCSI initiator software. Once you have the initiator and targets talking to each other the drives appear to each server as just another local hard disk. From the Windows Disk Administrator you can set them as basic or dynamic disks and use them individually or together in any RAID array that Windows supports.

To test the appliance we initially installed the iSCSI initiator software on a dual 1.7GHz Xeon server running Windows Server 2003 and logged on to a single iSCSI target drive. Using the open-source Iometer performance utility we assigned one disk worker to the drive. Utilising 64KB transfer requests and a 100 per cent sequential distribution we saw an average transfer rate of 33MB/sec. We then brought in three more servers using their own iSCSI targets and ran separate instances of Iometer, which reported a cumulative transfer rate of 99MB/sec. During this test we noted that processor power has a significant impact on throughput due to the demands of the iSCSI software - you can see these results in our review of Adaptec's iSCSI HBA (see p168). For the final test we configured four iSCSI targets on the dual Xeon server as a RAID-0 striped array and used the same Iometer configuration but with four disk workers assigned to the array and ten outstanding I/Os selected. Although this only returned 66MB/sec, it's worth noting that this is about 25MB/sec faster than the server's local Ultra320-based storage could deliver.

Our tests results show that iSCSI doesn't even come close to FC SANs for performance as revealed all too clearly by the Chaparral RIO eXp. However, its biggest strength is the much lower cost of implementation. As a backup accelerator, the REO RA2000 certainly delivers on its promise, which is precisely why our last backup tape drive group test used it as the main test platform.