This is the second of a series of posts reviewing the StarWind Enterprise Server iSCSI software target. The posts relate to version 4 of the product. Previous post(s) can be found at:
Review: StarWind Enterprise Server – Part I
In the first post of this review, I explained how StarWind’s server product provided the ability to turn a Windows server into an iSCSI storage device. In this post, I’ll focus more on the specific LUN types available to the user.
Image File Device – this type is a standard iSCSI LUN – fully occupying the disk space of the creation size. LUNs can be both compressed and encrypted, however it’s not clear from the documentation exactly how these features are implemented and to what security standards.
RAM Drive Device – an iSCSI LUN emulated purely in memory on the server. This device exists purely in memory on the server and so is a volatile device; if the power goes and the server reboots, then the data is lost. I’m not sure of the merits of this kind of device when the data is so transient.
Virtual DVD Device – this device type presents an ISO file as a iSCSI DVD-ROM device. This useful for sharing out ISOs across multiple clients; up to 16 may connect at any one time. One drawback though; the ISO file must exist on the local machine running StarWind, which is sort of limiting.
Disk Bridge Device – a passthrough device representing a single physical disk on the server. Think of this in the way RDM devices work on VMware – the device itself is virtualised through to the host.
Snapshot and CDP Device – this is an iSCSI LUN which supports Point In Time snapshots and thin provisioning. A LUN can be created from an existing device; either as a snapshot or full/linked clone. The thin functionality is pretty obvious (more on this in a moment). As for the CDP functionality, I had issues attaching this device type to my Windows client, which wouldn’t let me assign a drive letter to the LUN. In addition, the volume was already formatted as a raw device.
Mirror Device – an iSCSI LUN mirrored with RAID-1 or replicated to another server. Mirroring of the logical iSCSI LUN can be done on the local machine (providing some level of fault tolerance in a single server with multiple hard drives) or using a remote LUN on another server capable of presenting out iSCSI devices.
SPTI Device – a raw (non-emulated) version of a Disk Bridge Device. This is more closely aligned to an RDM device then the Disk Bridge type. All devices (including read-only media such as DVD-ROM) can be externalised as iSCSI devices.
Virtual Tape Device – an iSCSI LUN representing a tape device. This feature has been removed from the current product and is now available separately as StarWind VTL.
There’s not doubt the range of supported devices is comprehensive, although some features such as encryption and compression need more explanation to understand how they are implemented and how data could be recovered in a server failure scenario.
It’s pretty much taken for granted that thin provisioning needs to be provided as a feature in storage arrays, whether physical or virtual. Fortunately StarWind Server offers this as part of the CDP device type. As a test, I created an iSCSI thin LUN using the console and connected it to a Windows host. As expected, copying files to the LUN grew the device by the size of the copied files. Unfortunately, deleting the files and/or reformatting the drive did not reclaim the released space. In fact, a full format of the drive, rather than a quick format resulted in the full capacity of the drive being allocated and the benefits of thin provisioning wasted. (Tip: Use Quick format on Windows). In this release of the product there appears to be no way to reclaim unused resources within thin provisioned devices. Thin Provisioning implementations need to add this functionality as the value of using thin LUNs simply diminishes over time.
Overall, the product offers a wide range of device types. A more detailed understanding of some specifics (e.g. encryption standards) is required. Thin LUNs need some space release technology added to ensure thin doesn’t simply revert to thick over time.
In the next post, I’ll look at security, performance and the competition.
Disclaimer: I have no connection or relationship to StarWind Software. A free copy of the StarWind Server software was provided by the company for this evaluation.