On Wed, Apr 21, 2010 at 6:32 AM, Bill Davidsen <davidsen@xxxxxxx> wrote: > Michael Evans wrote: >> >> On Sun, Apr 18, 2010 at 8:46 PM, Kaushal Shriyan >> <kaushalshriyan@xxxxxxxxx> 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@xxxxxxxxxxxxxxx >>> 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 <davidsen@xxxxxxx> > "We can't solve today's problems by using the same thinking we > used 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" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
