Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Sat, Jun 02, 2012 at 02:02:03PM +0200, Wiebe Cazemier wrote: > ----- Original Message ----- > > From: "Florian Haas" <florian at hastexo.com> > > To: "Wiebe Cazemier" <wiebe at halfgaar.net> > > Cc: drbd-user at lists.linbit.com > > Sent: Friday, 1 June, 2012 9:03:42 PM > > Subject: Re: [DRBD-user] Performance hit DRBD vs raw block device, even when disconnected > > > > Sorry if I rant for a bit, but it's been _years_ since I wrote that > > part of the User's Guide, and it's been regurgitated a million times > > on this list, by myself and many others. Please, say it after me: > > > > I will not use dd without oflag=direct or oflag=dsync. > > I will not use dd without oflag=direct or oflag=dsync. > > I will not use dd without oflag=direct or oflag=dsync. > > > > You're kidding yourself. You're measuring *something*, a mix of > > caching effects and actual I/O, but not the throughput of your block > > device. > > > > Please rerun your tests with oflag=direct, and then come back with > > updated results. > > > > Florian > > Sorry, I should have realized that... > > Testing now yields more normal results: > > 1) about 25-30 MB/s on both nodes. > 2) Higher speeds (about 50 MB/s) when DRBD device is in disconnect mode. > > If I invalidate my test device (causing a resync), it syncs at about 60 MB/s, the speed I limited it to. I don't understand why normal throughput is so much lower. Fiddling with max-buffers, max-epoch-size and unplug-watermark doesn't really seem to influence the 25 MB/s much. > > To give more information about the hosts: > > Host1: Supermicro (mainboard: X8SIL-F). 3Ware 9650 SE SATA2 hardware RAID6, 5x 2TB disks. Xeon(R) CPU X3430, 2.40GHz. Machine is Xen dom0 and dom0 has 1 core. > > Host2: Dell Poweredge R200. 2x250GB Linux MD RAID1. Xeon CPU X3220, 2.40GHz. Machine is Xen dom0 and dom0 has 4 cores. > > Both nodes reach higher network and disk speeds then I'm getting here. Put DRBD meta data on RAID 1. Use decent battery backed (or otherwise non-volatile) write cache. Disable barriers and flushes in DRBD. -- : Lars Ellenberg : LINBIT | Your Way to High Availability : DRBD/HA support and consulting http://www.linbit.com