[DRBD-user] difference in speed when using external metadata

Mark Morlino mrmorlino at alaska.edu
Thu Jan 13 21:07:16 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Mon, Jan 10, 2011 at 10:31 AM, Bart Coninckx
<bart.coninckx at telenet.be> wrote:
> On Monday 10 January 2011 19:40:17 J. Ryan Earl wrote:
>> On Sun, Jan 9, 2011 at 10:03 AM, Bart Coninckx
> <bart.coninckx at telenet.be>wrote:
>> > Hi all,
>> >
>> > am reading the Novell docs on DRBD and one of the ways they mention to
>> > speed
>> > up DRBD is using external metadata. Possibly a hard question to answer
>> > but could someone indicate by what degree this would enhance speed
>> > (provided using
>> > a sufficient fast disk for the metadata, like a SSD)?
>> >
>> > thx!
>> >
>> > Bart
>> A RAID controller with a backed-write cache essentially nullifies
>> any advantage there.  A RAID controller that can instantly return on
>> FUA-writes is what you want.
>> -JR
> Hi,
> so the essence of your answer is that this is not a matter of having metadata
> internal or external, but rather of having the right RAID controller?
> Do you have examples of these in the major brands (HP, Dell, ...) ?
> thx!
> B.
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I would be interested in this information too (in my case I'd be
interested in any supermicro controllers that meet this requirement).
If I understand correctly, an FUA-write is a write-through request.
Doesn't that mean that the controller should not return until
everything has been physically written to the disk? It seems to me
that in order to return instantly on an FUA-write, the controller
would have to ignore the FUA request and return once the data has been
written to the cache. I don't see how it can both force physical disk
access and return instantly. Perhaps I'm missing something, it
certainly wouldn't be the first time.


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