Date: Thu, 26 May 2005 12:40:19 -0500 From: Eric Anderson <anderson@centtech.com> To: Bjoern Koenig <bkoenig@cs.tu-berlin.de> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Disable read/write caching to disk? Message-ID: <42960A03.6020001@centtech.com> In-Reply-To: <429606D9.6080602@cs.tu-berlin.de> References: <4295D51F.50106@centtech.com> <429606D9.6080602@cs.tu-berlin.de>
next in thread | previous in thread | raw e-mail | index | archive | help
Bjoern Koenig wrote: > 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" That appears to be for ata devices only, correct? I'm using fiber channel so it's scsi-like. > 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. Host A has filesystem mounted rw, host B has it mounted ro. If host A makes changes, host B cannot see them without unmounting and remounting ro. I wanted to find out if it was a read caching issue on host B. > You can mount partitions that I/O will done synchronously by adding the > option 'sync' to fstab. I've tried this. I'm not sure if it made any difference. >> 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. I've turned off softupdates to minimize my variables. > 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. I'll look again.. Thanks Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology A lost ounce of gold may be found, a lost moment of time never. ------------------------------------------------------------------------
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?42960A03.6020001>