Six iSCSI SANs unleashed
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Intransa claims that as many as six controllers may exist in a realm at a time; my tests were conducted on a pair of iSCSI controllers connected to a pair of 4TB disk arrays. Intransa's approach to disk connectivity is definitely different, but it also has the benefit of leveraging the connectionless basis of IP networking to permit dynamic capacity increases. To add another disk array to a realm can happen on the fly by simply cabling and powering up the new array -- the new storage is detected and seamlessly added to the realm, requiring no downtime.
The Intransa arrays are large in raw disk capacity, but because RAID 5 is not supported, the true capacity works out to be significantly less. RAID 0, 1, and 10 are the only supported RAID levels, but you can chose among those on a per-volume basis. This reduces the 4TB of raw disk in each array to 2TB. Only certain portions of available disks need be consumed by a volume. For instance, the creation of a new 250GB volume -- using default settings -- will use roughly half of four 250GB drives, placing the volume data on the outside sectors of each disk to maximize performance. This provides RAID 10 mirroring of a striped volume but uses only two spindles in each stripe. To overcome this limitation, Intransa has developed a policy-based disk allocation method. Available only through the CLI at the moment, this is a powerful tool, enabling admins to create specific policies governing disk allocation. An example might be to create a policy to maximize database performance by utilizing a minimum of eight disks with a specific stripe size. The custom policy can then be selected when creating a new volume.
The GUI is Java-based but is not delivered via browser, instead requiring installation on a Windows system. The UI is clean and relatively intuitive, but it lacks some human touches -- for instance, controllers are referred to by "module" names comprised of alpha characters and a MAC address, which makes referencing specific controllers needlessly difficult.
In the lab, I found performance under Windows to be truly abysmal, although the Linux numbers were quite respectable. This disparity was due to the fact that, by default, Windows does not sector-align primary partitions. By using Windows DiskPart to align the partition on a 4KB boundary, I was able to give the IP5500 a significant speed boost, suggesting that sector alignment is an absolutely required step for volumes created under Windows. This modification, however, introduced a problem with the Alacritech iSCSI accelerator -- causing abrupt volume log-offs -- that proved elusive to remedy.
Intransa has taken a truly unique approach to iSCSI storage, building some impressive features on IP concepts. The lack of redundant power in the controllers is a concern, as is the limited bandwidth available to each controller, but overall, the solution is elegant.