From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (mx1.redhat.com [172.16.48.31]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id l4D1YNC2032741 for ; Sat, 12 May 2007 21:34:23 -0400 Received: from mail.bmsi.com (www.bmsi.com [24.248.44.156]) by mx1.redhat.com (8.13.1/8.13.1) with ESMTP id l4D1YLjU010613 for ; Sat, 12 May 2007 21:34:21 -0400 Received: from bmsred.bmsi.com (bmsred.bmsi.com [192.168.9.50]) by mail.bmsi.com (8.13.6/8.13.6) with ESMTP id l4D1YG4G015400 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO) for ; Sat, 12 May 2007 21:34:16 -0400 Received: from localhost (localhost [127.0.0.1]) by bmsred.bmsi.com (8.13.5/8.13.5) with ESMTP id l4D1YGva027176 for ; Sat, 12 May 2007 21:34:16 -0400 Date: Sat, 12 May 2007 21:34:16 -0400 (EDT) From: "Stuart D. Gathman" Subject: Re: [linux-lvm] LVM on SATA/PATA disks In-Reply-To: <1179019386.15162.53.camel@pc.ilinx> Message-ID: MIME-Version: 1.0 Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit To: LVM general discussion and development On Sat, 12 May 2007, Brian J. Murrell wrote: > On Sat, 2007-05-12 at 21:12 -0400, Stuart D. Gathman wrote: > > > > The interrupt rate has nothing to do with the type of disk, and a lot to > > do with the controller. There is a CPU difference between $50 > > consumer IDE/SATA adapters, and $300 server grade IDE/SATA adapters. > > You'll want the controller to support fast DMA at minimum. > > I thought the biggest thing that SCSI had that IDE didn't was SCSI's > ability to shovel an ass-barn-load of data to a disk and the disk would > go deal with it, giving up the SCSI bus so that another disk could be > shovelled another ass-barn-load of data to go and deal with, and so on. > > ... > > The contrast with IDE (or PATA as I guess the trendy name is), again as > I always thought was that the IDE bus was not available for use while a > disk was still pending a media I/O operation, so that with multiple > devices, you could not leverage the I/O of the IDE bus using multiple > devices, essentially in parallel. I guess this is where having system > with multiple IDE buses and only putting a single device per bus grew > from. We always put exactly one IDE disk per channel for that very reason. You are correct that with 2 disks on the same channel, only one can be active at a time. So don't do that. A $50 IDE PCI card give you 2 IDE channels - for 2 disks in high performance mode (suitable for mirroring). Buy two cards for 4 disks. Or a $300 server card for 8 disks. > How does SATA fit in with all of this? Is it basically the same > limitations on the bus as IDE/PATA, so that you'd really not want to put > more than 1 device per bus? SATA mandates at most 1 disk per channel, making the issue moot. It is still true that there is only one active disk on a bus. But then there is only one disk on a bus. -- Stuart D. Gathman Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flammis acribus addictis" - background song for a Microsoft sponsored "Where do you want to go from here?" commercial.