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