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Re: CVS commit: src/lib/libc/sys
On Wed, Mar 25, 2009 at 08:58:18AM +0000, Andrew Doran wrote:
> > Log Message:
> > Update the note about sync returning before buffers are written: it is a
> > piece of historical behavior, not a current bug. Also, while here, add a
> > bit about disk write-back caches and point to dkctl/scsictl.
> > Bump date. (first time since 1993!)
> Thanks, however:
> +.Sh CAUTIONS
> +Many modern disks contain write-back caches.
> +In theory
> +.Fn sync
> +flushes these.
> This is not true, unless you are using logging (or zfs!).
It should be true; why is it not? Does this need to be moved under BUGS?
> +In practice there are many possible ways for this mechanism to go
> +It is prudent (where possible) to allow a few seconds after syncing
> +for everything to settle before e.g. turning off the power.
> +It may also be desirable to use
> +.Xr dkctl 8
> +.Xr scsictl 8
> +to disable the write-back cache entirely.
> This is wishy washy. It gives the sense that we know there is a problem, but
> simply couldn't be arsed fixing it. What do you want to convey?
Should we have a list of filesystems and whether they work properly?
Crossreferences to mount_foo(8) for all foo? Or should it just contain
Kirk's advice, that is, people who care about their data shouhld
always disable the write-back cache?
David A. Holland
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