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Date: 14 Jul 2005 18:09:07 -0400
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Subject: Re: dangerous situation with shutdown process
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Jon Dama <jd@ugcs.caltech.edu> writes:

> softupdates is perfectly safe with SCSI.
> 
> its well known that ide and sata w/wo ncq fails to provide suitable
> semantics for softupdates
> 
> however, journaling fairs no better, and request barriers do nothing to
> solve the problem.

I had assumed that the sequence of operations in a journal would be
idempotent.  Is that a reasonable design criterion?  [If it is, then
it would make up for the fact that you can't build a reliable
transaction gate.  That is, you would just have to go back far enough
that you *know* all of the needed journal is within the range you will
replay.  But even then, the journal would need to be on a separate
medium, one that doesn't have the "lying to you about transaction
completion" problem.]

> On Thu, 14 Jul 2005, Matthias Buelow wrote:
> 
> > Kevin Oberman wrote:
> >
> > >SCSI or ATA? If it's ATA, turn off write cache with (atacontrol(8) or
> > >the sysctl.
> >
> > You do NOT want to do that. Not only will performance drop brutally
> > (example: drop to 1/5th of normal write speed for sequential writes,
> > probably worse for random writes) but it will also significantly
> > reduce the lifetime of your disk. Modern disks are designed to be
> > used with the write-back cache enabled, so don't turn it off.

I have no idea what "designed to be used with the write-back cache
enabled" could affect the operating life of the disk.