Linked monitor capturing only a few frames

[carcachute]

I have ZM 1.27.99 on an Ubuntu 14 Server box. The computer is an Intel Atom D510 with 2GB of memory and a dedicated hard disk for recording.

I have four cameras:

• Three D-Link DCS-942L cameras running 640x480 @ 15fps and 320x240 @ 6fps simultaneously (MJPEG)
• One D-Link DCS-2230 running 1920x1080 @ 15fps and 480x270 @ 7fps simultaneously (MJPEG)

I have eight monitors: four for the low-resolution feeds to perform motion detection, and four on the high-resolution feeds triggered off the low-resolution feeds and set to NODECT mode.

All eight buffers are 100 frames long, and I have the before & after set to 100 frames on all monitors. I bumped the kernel's maximum shared memory segment size to 128MB and all the monitors light up green on the main status display.

I'm finding that, the linked triggering works as expected and events do appear in the high-resolution monitors. When I generate a long motion event, the entire event is captured correctly in the low-resolution monitor and playback works (but is of course poor quality). When I look at the linked monitor to get high-resolution playback, an event of similar length is generated, but contains only the first 2-3 frames. All the remaining frame thumbnails in the playback view are missing and playback proceeds for less than a second before stopping.

I noticed there was a recommendation not to exceed (buffer size)/2 for the "before" frame count. Is the risk that the buffer will overrun if the contents aren't removed on time and the contents get clobbered?

Thanks!