From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Linux RAID Partition Offset 63 cylinders / 30% performance hit? Date: Wed, 19 Dec 2007 12:40:55 -0500 Message-ID: <476957A7.5010805@tmr.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Justin Piszcz Cc: Mattias Wadenstein , linux-raid@vger.kernel.org, apiszcz@solarrain.com List-Id: linux-raid.ids Justin Piszcz wrote: > > > On Wed, 19 Dec 2007, Mattias Wadenstein wrote: > >> On Wed, 19 Dec 2007, Justin Piszcz wrote: >> >>> ------ >>> >>> Now to my setup / question: >>> >>> # fdisk -l /dev/sdc >>> >>> Disk /dev/sdc: 150.0 GB, 150039945216 bytes >>> 255 heads, 63 sectors/track, 18241 cylinders >>> Units = cylinders of 16065 * 512 = 8225280 bytes >>> Disk identifier: 0x5667c24a >>> >>> Device Boot Start End Blocks Id System >>> /dev/sdc1 1 18241 146520801 fd Linux raid >>> autodetect >>> >>> --- >>> >>> If I use 10-disk RAID5 with 1024 KiB stripe, what would be the >>> correct start and end size if I wanted to make sure the RAID5 was >>> stripe aligned? >>> >>> Or is there a better way to do this, does parted handle this >>> situation better? >> >>> From that setup it seems simple, scrap the partition table and use the >> disk device for raid. This is what we do for all data storage disks >> (hw raid) and sw raid members. >> >> /Mattias Wadenstein >> > > Is there any downside to doing that? I remember when I had to take my > machine apart for a BIOS downgrade when I plugged in the sata devices > again I did not plug them back in the same order, everything worked of > course but when I ran LILO it said it was not part of the RAID set, > because /dev/sda had become /dev/sdg and overwrote the MBR on the > disk, if I had not used partitions here, I'd have lost (or more of the > drives) due to a bad LILO run? As other posts have detailed, putting the partition on a 64k aligned boundary can address the performance problems. However, a poor choice of chunk size, cache_buffer size, or just random i/o in small sizes can eat up a lot of the benefit. I don't think you need to give up your partitions to get the benefit of alignment. -- 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