Date: Mon, 10 Mar 2003 07:54:53 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Nuno Teixeira <nunotex@aeiou.pt> Cc: freebsd-current@freebsd.org Subject: Re: softupdates && write cache && ata tags topic Message-ID: <3E6CB54D.A8A7F7F0@mindspring.com> References: <20030308151549.GA622@gw.tex.bogus>
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Nuno Teixeira wrote: > I understand the basic concept of the folowing techs: softupdates, disk > write cache and ata tags. > > My question is: > > It is safe to use softupdates + write cache + ata tags (IBM disk)? > > I read someware that it not safe to use softupdate + write cache > (without ata tags) and if it is not safe why FreeBSD 5.0 ships with them > enabled? See the discussion of 3 weeks ago with one of the engineers from Maxtor, on this list. The short answer is that the drive does not honor tags on a commit to stable storage, before returning the request as satisfied, and that's because on a write, ATA doesn't support disconnect with tagged commands. As to why write caching is on be default, there's a lot of going back and forth on that, and it's flipped state maybe 4-5 times, so far. The short answer is that ATA drives are pig-slow with write caching disabled, and users find that unacceptable. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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