High bandwidth disk management techniques
High bandwidth disk management techniques
- Subject: High bandwidth disk management techniques
- From: Mark Gilbert <email@hidden>
- Date: Sun, 1 May 2005 10:30:27 +0100
Folks.
I wonder if anyone can offer their experience in efficient techniques
for very disk intensive real time operations.
Our application reads audio from 64 or more files in real time, and
requires consistent performance. The total data throughput is only
about 10 megabytes per second, but unlike a single video file, using
64 audio files has its own seriously taxing load on the disk.
We have noticed that OSX seems to maintain a HUGE disk cache (as much
as 250 MB) which sits between our calls to disk and the actual disk
access (we call once per second, but the disk is only hit around once
every 5 seconds).
There are various aspects to the challenge - access time,
fragmentation, cache management and overall throughput. I wondered if
anyone has any experience on techniques to optimize this type of disk
access.
Currently our subsystem maintains a 1 second buffer for each audio
file, so we read about 200k once per second per file. This works OK
with lower track counts, but as we approach 64, we start to see
things stalling. We have tested with an internal SATA, and external
SCSI drive, and an XServe RAID. The SCSI drive seems to offer the
best performance, although it is still failing to deliver using our
current data handling techniques.
I was surprised to find that the RAID didn't help, even with 1GB of
cache. I think the problems is one of startup - getting the 'inertia
going' with the cache. If we let playback struggle along, eventually
it does sort itself out on all the drives tested. The problem we
have is getting the throughput established right from the start of
playback.
We do prepare the first second of audio in the buffers before we
start playing, but this doesn't seem to be enough to kick all the
caching into top gear.
I know this is a very specialised and complex question, but I
wondered if anyone who has experience with real time playback of
large numbers of disk streams could offer any general advice.
thanks
Mark Gilbert.
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