Date: Thu, 29 Jul 1999 02:10:09 -0700 From: David Greenman <dg@root.com> To: chrw <shredder@hack.babel.dk> Cc: freebsd-isp@FreeBSD.ORG Subject: Re: FreeBSD diskcache Message-ID: <199907290910.CAA06665@implode.root.com> In-Reply-To: Your message of "Thu, 29 Jul 1999 11:01:29 %2B0200." <Pine.BSF.3.95.990729105134.18576A-100000@hack.babel.dk>
next in thread | previous in thread | raw e-mail | index | archive | help
>Can someone enlightned me how the diskcache disk i/o performance is >achieved on freebsd? It seem, if one runs a find thru all the fs, >it will cache some, but not all of the fs. If one mounts >the fs with the asynch option, this was supposed to increase >performance/use of io disk cache. I tested this, and noticed no >difference, the disk cache appear to be of a fixed size, regardless >of available (free) memory, and regardless of a(sync) operations. Can >someone indepth explain this, in perspective of the linux way, with a >dynamic disk cache which inc/decreases the size of the diskcache this way >adapting to the current level of free memory, and this way enhancing >disk performance, and perhaps introducing problems regarding fs >corruption in a crash or heavy load situation (?). I think the best answer to this is that FreeBSD caches as much file data as possible and uses otherwise free memory for this purpose. Our filesystem buffer mechanism is very different from traditional Unix and serves only as a temporary mapping mechanism for pages in the virtual memory system where the file data is ultimately cached. The async option really has nothing to do with any of this. It's purpose is to defer writing of certain filesystem metadata (such as directories and inodes) so that the number of disk seeks can be reduced. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project - http://www.freebsd.org Creator of high-performance Internet servers - http://www.terasolutions.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199907290910.CAA06665>