THE ARCHIVE BLOG
April 13, 2016
It was just brought to our attention that openaxf.org is talking about the AXF interoperability trial we participated in. To quote them, “Earlier this month, Oracle (Front Porch Digital) and Digital Preservation Laboratories became the first vendors to successfully and independently exchange SMPTE standard Archive eXchange Format (AXF) Objects created by their respective storage management applications.”
If you haven’t already heard of AXF, it’s probably something you going to hear a lot about this year. A quick way to explain it in our environment is that it’s a comprehensive standard that allows the aggregation of disparate file elements associated with a feature film or episodic program into a single “Object” while allowing rich archiving-centric functionality such as embedded MD5 or SHA-1 in a OS/filesystem-neutral environment with seemingly limitless scale. I know, super cool, but that’s not the best part. What makes this awesome is that an incredible group of SMPTE Technical Standards Committee folks have volunteered an incredible amount of time over the past 10 years to make it a standard that any person or company can use (you do have to pay SMPTE a nominal fee to download the standard).
When I first heard of AXF, I immediately thought of TAR and LTFS and how it compared to these two other open-ish standards. It’s not really appropriate to compare it to those because, although it shares some aspects of those, it’s too different in what it does. TAR is a way to dump data to tape. The problem if you want one frame of your show off the tape you have to extract a lot more than you actually need. However, TAR is super fast. LTFS creates a filesystem on tape where you then put data. Sadly, we all know the interchange and shoe-shining problems that occur with LTFS collections.
AXF has the best parts of both TAR and LTFS. For example, if you just want one frame of your show off the tape, you don’t necessarily have to extract the entire AXF Object. The system will simply go to the beginning of the Object, find the location of the frame you need and you are good to go. You also get the benefit of determining the contents of a tape quickly by reading just the first bit of an AXF Object (and I should probably mention we create very large Objects…sometimes only one per tape). It’s true you could format an LTO tape as LTFS and then put an AXF Object on it but I think that would be more for studio interchange and not for long-term preservation.
Back to the original topic, Digital Preservation Labs and Oracle (Front Porch) completed the first successful cross compatibility testing and validated that all the hard work by the SMPTE Technical Standards Committee (who volunteer time, they aren’t paid to do this!) is paying off.
March 10, 2016
Welcome to the first of what we hope to be an ongoing series of entries that share some details of the projects we are working on and the lessons we all continue to learn. I thought I would talk a little bit about the difference between LVD and HVD SCSI buses and how they relate to legacy tape machines like DLT, Sony DTF and even the Ampex devices. LVD stands for low voltage differential whereas HVD stands for high voltage differential. HVD came first but LVD became more dominant as SCSI technology became more affordable and accessible to the ordinary consumer. They key advantage of the LVD technology is that it allowed for faster throughput in the SCSI chain (specifically due to the 3.3 volt range instead of a 5 volt range). Consequently, lower volts meant lesser heat compared to traditional HVD technology.
Here comes the misconception part. In the 1990s, I was in a machine room and was warned, “Don’t accidently put an LVD device on an HVD SCSI chain. You’ll fry the device!” I was actually terrified for years working from visual effects companies to post houses that I would accidently destroy the DTF or LTO machine. Well, after 20 years of fear, I no longer need to be paranoid. The truth is, no equipment will be harmed if you mismatch your voltage technology on SCSI buses. If you put a LTO-3 machine on an HVD bus designed for a Sony DTF machine, the LTO-3 will logically detach from the bus. If you place a Sony DTF (HVD) on a SCSI bus for an LTO-3 machine, the whole bus will become disabled (at least on Adaptec and LSI cards).