Re: Poor write performance with write-intent bitmap?

[John Robinson <john.robinson@anonymous.org.uk>]

On 22/04/2009 15:21, Andre Noll wrote:
> On 13:41, John Robinson wrote:
>>> Normal shutdown should put the raid in read-only mode as last step. At
>>> least Debian does that. That way even a mounted raid will be clean
>>> after reboot.
>> Yes, I would have thought it should as well. But I've just looked at 
>> CentOS 5's /etc/rc.d/halt and as far as I can see it doesn't try to 
>> switch md devices to read-only.
> 
> There's no need to do that in the shutdown script as the kernel will
> switch all arrays to read-only mode on halt/reboot.
> 
> Moreover, as raid arrays are automatically marked clean if no writes
> are pending for some small time period, a simple "sync; sleep 1"
> at the end of the shutdown script is usually enough to have a clean
> array during the next boot.

But that's still only "usually". Considering the enormous efforts taken 
to unmount filesystems (or remount them read-only) so they're certain to 
be clean at the next startup, it seems odd to settle for "usually"... 
and CentOS 5 doesn't even appear to do that.

Goswin, please can you tell me what command Debian uses? I think I want 
to combine both of these into my systems' halt scripts.

Cheers,

John.