On Wed, Feb 17, 2010 at 10:13 AM, Kristleifur Daðason <kristleifur@xxxxxxxxx> wrote: > Hi, > > I remember seeing some discussion on what sector a partition starts > on. Many programs create partitions that start on sector 63, which > doesn't really make any intuitive sense to me. I just lost a disk from > of a RAID10 array and was thinking I'd try to understand this issue as > I have to do some disk/block/partition wrangling anyway. > > From a discussion from linux-raid titled "Raid 10 LVM JFS Seeking > performance help", I found the following: > > On Mon, Dec 21, 2009 at 12:56 PM, Goswin von Brederlow > <goswin-v-b@xxxxxx> wrote: >> >> Also, on a lower level, make sure your raid does not start on a >> partition starting at sector 63 (which is still the default in many >> partitioning progs). That easily results in bad alignment causing 4k >> chunks to land on 2 sectors. But you need to test that with your >> specific drive to see if it really is a problem. >> > > Hmm ... In short: Do I want to have a partition start on any > particular sector? Especially in the case where I want to ... > - build a RAID10 with partitions (i.e. not with raw devices) > - using ~256K chunks > - and have a nice JFS filesystem on top of it. > > Starting on sector 64 feels conceptually "prettier" than Sector 63, > but I can't picture the case where it behaves any different. Except > perhaps when GRUB expects stuff to begin at sector 63, making a mess > if we're starting at sector 64. Though it *should* work OK, of course. > > Anyways ... Any tips on a subtle matter most well appreciated. > Especially tell me if I'm overthinking, please. Thanks. > > -- Kristleifur I believe a better choice is to start at 1 MB regardless of sector size. This was initiated by Vista moving to that a few years ago so you will almost always find hardware, etc. That assumes your sector size is still based on a power of two. If you do get a 4K sector drive be sure it is 1MB aligned (ie. Vista mode). The only shipping drives I know of are the WD ones and they have a jumper for sector 63 aligned and 1MB aligned. In a raid using sector 63 alignment would really make it hard to keep track of things. There are rumors the future drives may come from the factory pre-configured for one or the other, so if that turns into reality be sure to buy the 1MB aligned drives. Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer Preservation and Forensic processing of Exchange Repositories White Paper - <http://www.norcrossgroup.com/forms/whitepapers/tng_whitepaper_fpe.html> The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- 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
