Re: High bandwidth disk management techniques
Re: High bandwidth disk management techniques
- Subject: Re: High bandwidth disk management techniques
- From: Mark Gilbert <email@hidden>
- Date: Tue, 3 May 2005 21:59:01 +0100
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The issue nobody has mentioned here -- and by far the nastiest one --
is allocation.
When do you do it during writes? Do you pre-allocate before starting
recording or allocate new disk blocks on the fly? OS 9 pretty much
require pre-allocation. Is OS X better in this regard? I don't
actually have much experience doing high track count recording on OS
X, yet.
How to get as much contiguous allocation as possible?
In fact we don't do any pre-allocation. There is no problem with
recording 64 tracks to disk without pre-allocation. Record
performance was never a problem - it was all about the playback.
At one point, I did wonder if the problems we were seeing were
related to the inevitable fragmentation on disk when writing to 64
files with no pre-allocation. We observe the OS writing only once
per 5 seconds, so I wonder if the caching is actually avoiding the
fragmentation in practice. I haven't actually checked to see how
fragmented the files ended up.
To clarify - we discovered that the main problem we were having was
related to Virtual Memory. As we went into play, we allocated lots
of memory, and it was the VM paging which actually stalled the start
of our playback. Ironically, using SMALLER buffers turned out to be
the solution (needed less VM traffic).
Cheers
MarK Gilbert
--
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