Date: Tue, 27 Feb 1996 22:40:23 -0700 From: Nate Williams <nate@sri.MT.net> To: adrian@virginia.edu Cc: Peter Stubbs <peters@staidan.qld.edu.au>, Peter van Heusden <pvh@leftside.its.uct.ac.za>, freebsd-fs@freebsd.org Subject: Re: Compressing filesystem for FreeBSD Message-ID: <199602280540.WAA06665@rocky.sri.MT.net> In-Reply-To: <Pine.SUN.3.90.960227210012.29395A-100000@stretch.cs.Virginia.edu> References: <6BD18783D77@aidan.staidan.qld.edu.au> <Pine.SUN.3.90.960227210012.29395A-100000@stretch.cs.Virginia.edu>
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> > The real problem with compressing a file system that is often > forgotten is that you are increasing the cost in CPU cycles for a disk > I/O. I don't think it's at all forgotten. I think that folks are willing to take the performance hit for the decrease in disk space for files that are rarely accessed. > While I have had dos/linux enthusiasts go on about how compressing > your filesystem can both improve I/O bandwidth and increase available disk > space, the cost is often fogotten. While I do know that compressed FS often do increase I/O under DOS due to stupid disk layouts, I haven't heard many 'compression' proponents claim that it increases I/O on real FS. > On a multi-user system, the CPU is not idle during disk I/O. Depends. On my SCSI system it might be, depending on the load. > I think there would also be problems with paging and reads in general. > Which block of the disk contains the nth byte? In short, I don't see > it being worth the effort. On my laptop it would *certainly* be worth the effort. I've got cycles to burn since I'm the only user, and I'm more than willing to get free disk space for my cycles. On my multi-user system, I'm more than willing to take the performance hit for our local archives which are rarely accessed by take up a huge amount of space. I think most folks who are serious about this understand the costs, and are willing to pay them for certain applications. Nate
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