Re: Improvements to fsck performance in -current ...?

From: Terry Lambert (tlambert2_at_mindspring.com)
Date: 10/02/03

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    Date: Thu, 02 Oct 2003 10:02:43 -0700
To: Jens Rehsack <rehsack@liwing.de>

    Jens Rehsack wrote:
    > Kevin Oberman wrote:
    > > Current has two major changes re speeding up fsck.
    > >
    > > The most significant is the background operation of fsck on file
    > > system with soft updates enabled. Because of the way softupdates
    > > works, you are assured of metadata consistency on reboot, so the file
    > > systems can be mounted and used immediately with fsck started up in
    > > the background about a minute after the system comes up.
    >
    > Be careful what you promise :-)
    > Most new disks have an own disk cache and some of them have a
    > write cache enabled. In case of a hardware failure (or power
    > failure) this data may get lost and the disk's metadata isn't
    > consistent. It's only when no write cache below the system
    > is active.

    Actually, write caching is not so much the problem, as the disk
    reporting that the write has completed before the contents of
    the transaction saved in the write cache have actually been
    committed to stable storage.

    Unfortunately, IDE disks do not permit disconnected writes, due
    to a bug in the original IDE implementation, which has been
    carried forward for [insert no good reason here].

    Therefore IDE disks almost universally lie to the driver any
    time write caching is enabled on an IDE drive.

    In most cases, if you use SCSI, the problem will go away.

    -- Terry
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