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Re: CVS commit: src/lib/libc/sys

On Wed, Mar 25, 2009 at 05:32:52AM +0000, David A. Holland 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:

+Many modern disks contain write-back caches.
+In theory
+.Fn sync
+flushes these.

This is not true, unless you are using logging (or zfs!).

+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?

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