Re: [ANNOUNCE] DualFS: File System with Meta-data and Data Separation

From: Bill Davidsen
Date: Fri Feb 16 2007 - 18:46:08 EST

JÃrn Engel wrote:
On Thu, 15 February 2007 23:59:14 +0100, Juan Piernas Canovas wrote:
Actually, the version of DualFS for Linux 2.4.19 implements a cleaner. In our case, the cleaner is not really a problem because there is not too much to clean (the meta-data device only contains meta-data blocks which are 5-6% of the file system blocks; you do not have to move data blocks).

That sounds as if you have not hit the "interesting" cases yet. Fun
starts when your device is near-full and you have a write-intensive
workload. In your case, that would be metadata-write-intensive. For
one, this is where write performance of log-structured filesystems
usually goes down the drain. And worse, it is where the cleaner can
run into a deadlock.

Being good where log-structured filesystems usually are horrible is a
challenge. And I'm sure many people are more interested in those
performance number than in the ones you shine at. :)

Actually I am interested in the common case, where the machine is not out of space, or memory, or CPU, but when it is appropriately sized to the workload. Not that I lack interest in corner cases, but the "running flat out" case doesn't reflect case where there's enough hardware, now the o/s needs to use it well.

The one high load benchmark I would love to see is a web server, running tux, with a load over a large (number of files) distributed data set. The much faster tar create times posted make me think that a server with a lot of files would benefit, when CPU and memory requirements are not a bottleneck.

Bill Davidsen <davidsen@xxxxxxx>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot

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