From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Evans Subject: Re: RAID5 Date: Wed, 21 Apr 2010 12:43:05 -0700 Message-ID: References: <4BCEFE66.6010607@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4BCEFE66.6010607@tmr.com> Sender: linux-raid-owner@vger.kernel.org To: Bill Davidsen Cc: Kaushal Shriyan , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, Apr 21, 2010 at 6:32 AM, Bill Davidsen wrote= : > Michael Evans wrote: >> >> On Sun, Apr 18, 2010 at 8:46 PM, Kaushal Shriyan >> wrote: >> >>> >>> Hi >>> >>> I am a newbie to RAID. is strip size and block size same. How is it >>> calculated. is it 64Kb by default. what should be the strip size ? >>> >>> I have referred to >>> http://en.wikipedia.org/wiki/Raid5#RAID_5_parity_handling. How is >>> parity handled in case of RAID 5. >>> >>> Please explain me with an example. >>> >>> Thanks and Regards, >>> >>> Kaushal >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-rai= d" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.htm= l >>> >>> >> >> You already have one good resource. >> >> I wrote this a while ago, and the preface may answer some questions >> you have about the terminology used. >> >> http://wiki.tldp.org/LVM-on-RAID >> >> However the question you're asking is more or less borderline >> off-topic for this mailing list. =A0If the linked information is >> insufficient I suggest using the Wikipedia article's links to learn >> more. >> > > I have some recent experience with this gained the hard way, by looki= ng for > a problem rather than curiousity. My experience with LVM on RAID is t= hat, at > least for RAID-5, write performance sucks. I created two partitions o= n each > of three drives, and two raid-5 arrays using those partitions. Same b= lock > size, same tuning for stripe-cache, etc. I dropped an ext4 on on arra= y, and > LVM on the other, put ext4 on the LVM drive, and copied 500GB to each= =2E LVM > had a 50% performance penalty, took twice as long. Repeated with four= drives > (all I could spare) and found that the speed right on an array was ro= ughly > 3x slower with LVM. > > I did not look into it further, I know why the performance is bad, I = don't > have the hardware to change things right now, so I live with it. When= I get > back from a trip I will change that. > > -- > Bill Davidsen > =A0"We can't solve today's problems by using the same thinking we > =A0used in creating them." - Einstein > > This issues sounds very likely to be write barrier related. Were you using an external journal on a write-barrier honoring device? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html