LectureCapture.com: Capture Appliance Storage - LectureCapture.com

Just how many captures can this thing hold, anyway?

A little background: the Echo360 Capture Appliance is a network-dependent device. If you've ever used one, you know that it needs to talk to your ESS so it can upload your recordings. What you may not know is how it behaves when it isn't connected to your network. Outages happen—but what happens to your captures when they do? Does it eventually fill up?

The really short answer: no.

The not-so-short answer: it depends.

The appliance has a total of 20 gigabytes allocated for capture storage, but even the longest captures that the appliance can generate will never occupy that entire volume in one go. Longer captures will need more space than shorter ones, obviously. Although it is impossible to predict exactly how much space a capture will occupy on the disk because we encode at a bit rate proportional to the signal complexity (cf. CBR versus constant quantization), the appliance can contain as many as forty one-hour captures in its archive.

Why do we archive captures on the appliance? Simple: backups. We can hold them there, so we do. If something happens to the data immediately after upload (say, for example, you have a sudden power outage and the write cache for your ESS storage volumes didn't get committed to disk—ouch!), we can go back to the appliance and re-upload it. The question here is just how big the safety net is.

This archive does work like a FIFO buffer, getting rid of the oldest content to make room for the newest content. This is the only way captures can be deleted from the device. In the space of a single day, it's actually pretty difficult to generate enough capture data to clobber the archive of something you had captured earlier that morning. How far back the archive goes depends entirely on how the appliance is used.

If the appliance is offline during or after a capture, it won't actually move the capture into the archive until it's successfully uploaded it to the ESS, and it will keep retrying that upload until a network connection is available. The ESS may mark the capture as "Missed" until the appliance manages to do that, but then it should process normally. If you did somehow manage to capture a lot of content over a few days without ever connecting the device to the network, however, eventually you would reach the limit of the appliance's capacity and end up with capture losses. Again, it's hard to say exactly how many captures it would take to reach that limit, but it is something to be aware of if the appliance isn't allowed to flush those out often enough.

The current contents of the appliance's archive can be found by visiting its ad hoc control interface with a "/diagnostics" path element after the hostname (in ESS 2.5, we changed this to "/advanced", but the old one still works). There is a recovery option for re-uploading saved content from here, which lists every capture in the appliance by name.

Finally,the upload behavior of the appliance does change during captures. It throttles down the transfer speed considerably while captures are in progress in order to minimize the CPU overhead and give the capture task priority. Disabling SFTP encryption on the ESS will tend to speedup these transfers across the board because encryption requires more CPU time.

What this all means is this: if you aren't online with it, you can expect to be able to capture a reasonable number of presentations before the appliance risks data loss. The disk itself actually has a good chunk of space (~12-32 GiB, depending on when the appliance was manufactured) that isn't pre-allocated to anything at all, just in case we hit the soft limit. So long as you pay attention to your usage in these offline scenarios, you will have a very good idea of how fast content does cycle through your appliance.