From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: One Large md or Many Smaller md for Better Peformance? Date: Sun, 20 Jan 2008 17:18:40 -0500 Message-ID: <4793C8C0.3010301@tmr.com> References: <4793AE0E.609@pobox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4793AE0E.609@pobox.com> Sender: linux-raid-owner@vger.kernel.org To: Moshe Yudkowsky Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Moshe Yudkowsky wrote: > Question: with the same number of physical drives, do I get better > performance with one large md-based drive, or do I get better > performance if I have several smaller md-based drives? > > Situation: dual CPU, 4 drives (which I will set up as RAID-1 after > being terrorized by the anti-RAID-5 polemics included in the Debian > distro of mdadm). > > I've two choices: > > 1. Allocate all the drive space into a single large partition, place > into a single RAID array (either 10 or 1 + LVM, a separate question). > One partitionable RAID-10, perhaps, then partition as needed. Read the discussion here about performance of LVM and RAID. I personally don't do LVM unless I know I will have to have great flexibility of configuration and can give up performance to get it. Other report different results, so make up your own mind. > 2. Allocate each drive into several smaller partitions. Make each set > of smaller partitions into a separate RAID 1 array and use separate > RAID md drives for the various file systems. > > Example use case: > > While working other problems, I download a large torrent in the > background. The torrent writes to its own, separate file system called > /foo. If /foo is mounted on its own RAID 10 or 1-LVM array, will that > help or hinder overall system responsiveness? > > It would seem a "no brainer" that giving each major filesystem its own > array would allow for better threading and responsiveness, but I'm > picking up hints in various piece of documentation that the > performance can be counter-intuitive. I've even considered the > possibility of giving /var and /usr separate RAID arrays (data vs. > executables). > > If an expert could chime in, I'd appreciate it a great deal. > > -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark