Re: Removing softdep

[Gary Thorpe <gathorpe79%yahoo.com@localhost>]

--- On Wed, 6/11/08, Thor Lancelot Simon <tls%rek.tjls.com@localhost> wrote:

> From: Thor Lancelot Simon <tls%rek.tjls.com@localhost>
> Subject: Re: Removing softdep
> To: "Gary Thorpe" <gathorpe79%yahoo.com@localhost>
> Cc: tech-kern%netbsd.org@localhost
> Received: Wednesday, June 11, 2008, 10:32 AM
> On Tue, Jun 10, 2008 at 08:42:24PM -0700, Gary Thorpe wrote:
> 
> [Big block of text with no newlines!  Please, format your
>  messages to the NetBSD mailing lists so they break before
> the 80th column!]

I don't control this.

> > 
> > Someone else mentioned turning the write-cache off
> (which severely
> > reduces disk performance in some case) but for disks
> with tagged
> > command queueing that works properly, you can leave it
> on (most
> > commodity disks do not have tagged command
> queueing--that is for
> > SCSI/SAS or higher-end SATA).
> 
> The paragraph above is basically wrong.  It is not the case
> that if
> a drive supports tagged command queueing, you can safely
> allow it to
> cache all writes.  Rather, you can disable the write cache
> but get much
> the same benefit from the write deferral performed by the
> command queueing
> mechanism.

If the write-cache is enabled, when will the drive send the completion: when 
the data has been cached or when it is on the physical disk?



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