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- Terabyte capacity;
- RAID protection as standard;
- dynamic volume assignment and expansion;
- fast snapshot facility with scheduling option
- Complex deployment;
- requires specialised iSCSI host adapter to limit impact on host processor
Like the curate’s egg, Adaptec’s iSA1500 Storage Array is good in parts. The good parts are the terabyte of storage space available on this iSCSI appliance which can be carved up and shared across multiple servers connected to a standard Ethernet network. Added to which there’s hardware-based RAID protection, the ability to take multiple point-in-time snapshots and assign extra capacity on the fly. The not so good parts, however, are the complexity of the solution and the extra hardware needed in order to match the performance provided by a conventional Fibre Channel SAN.
In terms of hardware the iSA1500 is effectively a 1U rack-mount server based on a SuperMicro motherboard fitted with a 1.6GHz Intel Xeon processor and 1GB of memory. Four hot-swap 250GB Maxtor SATA disks provide the storage space, cabled to an Adaptec 4-port 2410SA storage controller which adds support for RAID levels 0,1,5 and 10. A pair of Gigabit Ethernet ports connects the appliance to the network with a separate 10/100Mbps Ethernet controller for management.
With its robust Linux-based OS, the iSA1500 boots quickly enough but setup thereafter is somewhat lengthy and involved. To start with you have to assign suitable IP addresses using a local terminal and serial port CLI (Command Line Interface) and can carry on with this if you want. However, most users will prefer Adaptec’s Web-based Storage Manager console, which can be installed on a Windows host and accessed remotely via a browser.
Unfortunately, before Storage Manager can be installed you have to download and install Microsoft’s iSCSI initiator and, if you're running Windows 2000, a command line utility called DiskPart. Moreover, because iSCSI shares data at the block level rather than file by file, (as with Network Attached Storage or NAS), the iSCSI initiator and an Adaptec agent also have to be loaded onto every server or workstation requiring access to the iSA1500 storage.
It took us quite a while to gather all this software together and get it installed, and it didn’t stop there. We then had to assign the disks to one or more storage pools and divide these up into separate iSCSI targets that, ultimately, became individual volumes on our network test servers. Once that was done, though, the iSCSI targets could be treated as if they were local disks with the added advantage that they were easy to expand in size. The later stages of deployment can also be automated, and it takes just a few seconds to take snapshots that can be used both for backup and to recover lost data very quickly indeed.
Overall performance is hard to measure on a product like this. One limiting factor is the use of SATA hard disks, which are cheaper than SCSI but not quite as quick. Another is network bandwidth, and yet another the speed of the processor(s) on the host server. Indeed, for maximum throughput it’s best to install a dedicated adapter, such as Adaptec’s 7211C (around £350 ex. VAT), to offload the IP and iSCSI processing work. Likewise, a dedicated gigabit network for iSCSI storage is recommended, both for maximum throughput and to limit the impact on LAN bandwidth.
That said, we obtained good results on our test network: even with an ageing Pentium III-based server and a single 10/100Mbps Ethernet adapter, the iSA1500 out-performed the local SCSI disks. The improvement on a more capable dual Xeon server was less marked however, and without a dedicated iSCSI adapter we were unable to get near the throughput levels of a Fibre Channel SAN.
Still, with no need for special networking hardware, the iSA1500 is a lot cheaper to deploy than a Fibre Channel SAN and, for those prepared to work through the installation issues, is worth considering as a means of providing impressively fast and very flexible shared network storage.