i have had this problem for quite a while and i am really getting desperate since i already got complete new hardware and still no change... PLEASE PLEASE PLEASE, someone please help me!!! (yes, i AM desperate, sorry.)
i work on something like a video recorder: i write live camera input to a .jxf-file-image-sequence on a ssd drive - it's quite a large buffer and i can easily store about half an hour of footage (720p50 greyscale, that comes down to 95.000 .jxf files, each 922 KB).
at the same time i read out that sequence (at random points) and render it to a jit.window with some overlays too it, almost all rendered on the gpu side.
as the disk buffer fills and writes the files for the first time i get full 50 frames read and write (yeah!).
however, once the disk buffer is filled completely and max starts overwriting old .jxf-files, the speed drops to half, resulting in about 25 fps.
some more background info:
- the system is based on fast thunderbolt-ssds which are capable of writing/reading a tenfold of the required data rate and faster ssds actually do not make much of a difference. it does work however if i write to a ramdisk (with a much smaller buffer though).
- i use a single qmetro at 2 ms that feeds into the jit.qt.grab (@unique) followed by a trigger which sends the timing to jit.gl.render and all other parts of the patch.
- the total buffer size does not make any difference - as long as it is bigger then my 16 gb of ram, otherwise the system caches to ram and all works fine.
- i see in the activity monitor, that the data read actually doubles as soon as overwriting starts. but as said, it's not even close to maxing out these drives and cpu load is minimal. it seems like max is reading out every file which gets overwritten first and only then writes to it in a separate process thereby cutting the framerate in half.
if helpful i'll gladly send along a stripped down version of my patch.
again, i'm really fighting with this for ages and already tried zillions of things - if anyone can help me out, i'll get him a crate of beer of wine or whatever!