[OpenAFS] memcache or diskcache on ramdisk

[Kris Van Hees]

On Thu, Dec 02, 2004 at 12:24:25AM +0100, EC wrote:
> Do using memory cache for AFSD 'better' (faster, more stable, etc..) than
> disk cache over RAMDISK or TMPFS ?

I haven't particularly attempted to use a disk cache on ramdisk or tmpfs, but
my guess would be that in those circumstances you are better off with memory
cache, since when using a disk cache, at startup you incur a penalty when it
tries to determine what is in the disk cache (since it is considered a
persistent cache).  Since you would end up starting up with an empty disk cache
the AFS client needs to reinitialize the various chunk files it creates in the
disk cache partition.  I have no idea how that measures up to any processing
that is done to initialize the memory cache, but my gut feeling would be that
the memory cache handles it more efficiently, since it doesn't have to bother
with the IO layer of the OS (even when the IO layer ends up working with a RAM
based filesystem anyway).

It would be interesting to see some actual performance comparison numbers
though.

	Kris