From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: RAID5 Date: Wed, 21 Apr 2010 09:32:22 -0400 Message-ID: <4BCEFE66.6010607@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: Michael Evans Cc: Kaushal Shriyan , linux-raid@vger.kernel.org List-Id: linux-raid.ids 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-raid" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> > > 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. If 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 looking for a problem rather than curiousity. My experience with LVM on RAID is that, at least for RAID-5, write performance sucks. I created two partitions on each of three drives, and two raid-5 arrays using those partitions. Same block size, same tuning for stripe-cache, etc. I dropped an ext4 on on array, and LVM on the other, put ext4 on the LVM drive, and copied 500GB to each. 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 roughly 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 "We can't solve today's problems by using the same thinking we used in creating them." - Einstein