Date: Thu, 26 May 2005 19:26:49 +0200 From: Bjoern Koenig <bkoenig@cs.tu-berlin.de> To: Eric Anderson <anderson@centtech.com> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Disable read/write caching to disk? Message-ID: <429606D9.6080602@cs.tu-berlin.de> In-Reply-To: <4295D51F.50106@centtech.com> References: <4295D51F.50106@centtech.com>
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Eric Anderson wrote: > Is it possible to disable all read and write caching to a disk? You can disable write the cache by adding the line hw.ata.wc="0" to /boot/loader.conf. I'm not sure if there are methods to disable the read cache of the hard disk drive. I can't imagine that the read cache is relevant concerning file system consistency. You can mount partitions that I/O will done synchronously by adding the option 'sync' to fstab. > Also - what exactly are the issues with forcing an unclean filesystem to > mount rw? I know you could (will?) have data corruption, but on which > data? Only data that has not been synced to disk? Any random amount of > data? If you use soft updates, then you will notice that some files disappear. This is not corruption, but rather a loss. In theory you won't have corruption under certain circumstances, practically it's a controversial issue. My machine crashes around three or four times a week for the last four month and I still don't have serious problems with the filesystem consistency. Read more about soft updates in the handbook: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-disk.html#SOFT-UPDATES There are some discussions about this topic in the mailing list archive. Regards Björn
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