From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mescal.linbit (office.linbit [213.229.1.138]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (No client certificate requested) by mail.linbit.com (LINBIT Mail Daemon) with ESMTP id ED140162A8 for ; Tue, 31 Jan 2006 19:00:14 +0100 (CET) From: Philipp Reisner To: drbd-dev@lists.linbit.com Date: Tue, 31 Jan 2006 19:00:15 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200601311900.15806.philipp.reisner@linbit.com> Subject: [Drbd-dev] internal vs external meta data [reminder] List-Id: Coordination of development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , internal vs external meta data Theoretical it should be quicker in case you use external meta data. Because AL-misses cause the disk-head to seek to the meta- data area, write to the AL, and then seek back to the data location. Real world measurement shows that the opposite is currently the case: internal meta data 257 misses (outer sectors) 19.62 MB/sec (1077936128 B / 00:52.390089) 19.28 MB/sec (1077936128 B / 00:53.314101) 19.31 MB/sec (1077936128 B / 00:53.229198) 0 misses (outer sectors) 20.72 MB/sec (1077936128 B / 00:49.611017) 20.95 MB/sec (1077936128 B / 00:49.074782) 20.77 MB/sec (1077936128 B / 00:49.502596) external meta data: 257 misses (outer sectors) 16.40 MB/sec (1077936128 B / 01:02.677786) 16.32 MB/sec (1077936128 B / 01:02.994084) 16.51 MB/sec (1077936128 B / 01:02.271167) 0 misses (outer sectors) 16.46 MB/sec (1077936128 B / 01:02.453234) 16.51 MB/sec (1077936128 B / 01:02.261244) 16.69 MB/sec (1077936128 B / 01:01.606018) With the write to the meta-data the disk queue runs more frequent, in case the meta-data is internal, this causes the higher performance because in the same disk queue are also the blocks for the data area. Completely unclear is why the two test sets with no misses completed with different results. The only difference was the location of the meta data, but there are now writes to the meta-data area, if there are no misses.=20 =2Dphilipp =2D-=20 : Dipl-Ing Philipp Reisner Tel +43-1-8178292-50 : : LINBIT Information Technologies GmbH Fax +43-1-8178292-82 : : Sch=F6nbrunnerstr 244, 1120 Vienna, Austria http://www.linbit.com :