Yet, despite ARCserve showing a popup which says "Restoration Successful", it restores up to the first 32KB of every file on the tape, but NO MORE."

From 10,000 feet, this sounds suspiciously like ARCserve is reading a single tape block or transfer buffer's worth of data for each file, writing out the result, then failing and proceeding to the next file.

Success popup notwithstanding, I'd expect to find errors in either the ARCserve or Windows event logs in this case — were there none?

While it's been decades since I've dealt with ARCserve specifically, I've seen similar behavior caused by any number of things. Off the top of my head,

(1) Incompatibilities between OS / backup software / HBA driver / tape driver.

In particular, if you're using a version of Windows much newer than Windows 2000, try a newer version of ARCserve.

In the absence of specific guidance, I'd probably start with the second* ARCserve version that officially supports Windows Server 2003:

(a) Server 2003 made changes to the SCSI driver architecture that may not be 100% compatible with older software.

(b) The second release will likely fix any serious Server 2003 feature-related bugs the first compatible version may have shipped with, without needing to install post-release patches that may be hard to find today.

(b) Significantly newer ARCserve versions are more likely to introduce tape drive / tape format incompatibilities of their own.

(2) Backup software or HBA driver settings incompatible with the hardware configuration (e.g., if ARCserve allows it, try reducing the tape drive transfer buffer size or switching from fixed block (= multiple tape blocks per transfer) to variable block (= single tape block per transfer) mode; if using an Adaptec HBA, try increasing the value of /MAXIMUMSGLIST[1]).

(3) Shitty modern HBA driver support for tape (and, more generally, non-disk) devices.

For example, modern Adaptec Windows HBA drivers have trouble with large tape block sizes that AFAIK cannot be resolved with configuration changes (though 32 kB blocks, as likely seen here, should be fine).

In my experience with PCIe SCSI HBAs, LSI adapters are more likely to work with arbitrary non-disk devices and software out-of-the-box, whereas Adaptec HBAs often require registry tweaks for "unusual" circumstances (large transfer sizes; concurrent I/O to >>2 tape devices; using passthrough to support devices that lack Windows drivers, especially older, pre-SCSI 2 devices), assuming they can be made to work at all.

LSI20320IE PCIe adapters are readily available for $50 or less on eBay and, in my experience, work well for most "legacy" applications.

(To be fair to Adaptec, I've had nothing but good experiences using their adapters for "typical" applications: arbitrary disk I/O, tape backup to popular drive types, CD/DVD-R applications not involving concurrent I/O to many targets, etc.)

(4) Misconfigured or otherwise flaky SCSI bus.

In particular, if you're connecting a tape drive with a narrow (50-pin) SCSI interface to a wide (68-pin) port on the HBA, make sure the entire bus, including the unused pins, are properly terminated.

The easiest way to ensure this is to use a standard 68-pin Ultra320 cable with built-in active LVD/SE termination, make sure termination is enabled on the HBA, disabled on the drive, that the opposite end of the cable from the built-in terminator is connected to the HBA, and, ideally, that the 68-to-50-pin adapter you're using to connect the drive to the cable is unterminated.

You can also use a 50-pin cable connected to the HBA through a 68-to-50-pin adapter, but then you're either relying on the drive properly terminating the bus — which it may or may not do — or else you need an additional (50-pin) terminator for the drive end, which will probably cost as much as a Ultra320 cable with built-in termination (because the latter is a bog-standard part that was commonly bundled with both systems and retail HBA kits).

Note that I have seen cases where an incorrect SCSI cable configuration works fine in one application, but fails spectacularly in another, seemingly similar application, or even the same application if the HBA manages to negotiate a faster transfer mode. While this should be far less likely to occur with a modern Ultra160 or Ultra320 HBA, assume nothing until you're certain the bus configuration is to spec (and if you're using an Ultra2 or lower HBA, consider replacing it).

With all that said, reversing the tape format may well be easier than finding a compatible OS / ARCserve / driver / HBA combination.

In any case, good job with that, and thanks for publishing source code!

[1] http://download.adaptec.com/pdfs/readme/relnotes_29320lpe.pd...