Re: Disable read/write caching to disk?

From: Eric Anderson (anderson_at_centtech.com)
Date: 05/26/05

  • Next message: Bjoern Koenig: "Re: Disable read/write caching to disk?" 
    Date: Thu, 26 May 2005 12:40:19 -0500
To: Bjoern Koenig <bkoenig@cs.tu-berlin.de>

    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.
------------------------------------------------------------------------
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  • Next message: Bjoern Koenig: "Re: Disable read/write caching to disk?"

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