[mythtv-users] How many simultaneous recordings on one drive?
linux at thehobsons.co.uk
Wed Sep 28 22:28:10 UTC 2011
Eric Sharkey wrote:
>Four recordings at 2 MB/s is 8MB/s. The buffers on these drives are
>usually 32 or 64MB. They can seek at almost 100Hz. It just won't be
>a problem. You've got a 1996 mind set here.
They may have large buffers, but then Myth is actively syncing each
record stream every second. I believe that should have the kernel
sending the write requests to the disk AND waiting for confirmation
that they've been written. That's immediately added several
seeks/second to write each stream plus the filesystem data.
Also, something not mentioned, if you are commflagging then that can
impose significantly higher I/O loadings than just streaming
recordings on/off disk.
Now I've got a machine dedicated to the backend, I've configured to
start commflagging when a recording starts (only one job at the
moment - need to experiment to see if two works well). The idea is
that it can process the data as it's received, and so can work from
what's already held in the OS cache and thus not add to the I/O load
by reading a recording in after it's finished.
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