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From John Plevyak <>
Subject Re: Question about disk optimization in ATS.
Date Wed, 14 Dec 2011 21:50:59 GMT
> Basically, for every 8KB of disk cache, one directory entry is created.
> And each directory entry consumes memory (10 bytes if I recall). So, if you
> average object sizes are much larger than e.g. 8KB, it's worthwhile to tune
> this setting. Likewise if your average objects are much smaller than 8k.
> There's also some overhead when ATS "syncs" this directory to disk (the
> larger the directory, the more disk I/O to sync it to disk).

Yes, the main overhead is that large disks are going to spend more time
syncing the directory.  You probably don't need tons of multi-terabyte
disks unless you are doing large documents (e.g. video) in which case you
could change that configuration to decrease the directory size.  6x146GB
just as separate disks should have good performance in most scenarios
(Zipf-ish distribution and working set comfortably within the 800GB).

> Don't ask me why the default is 8000 and not 8192, John might know :).

No reason.

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