On Dec 4, 2007 1:49 PM, Aaron Kulkis <[EMAIL PROTECTED]> wrote: > Chris Worley wrote: > > On Dec 4, 2007 10:22 AM, Jc Polanycia <[EMAIL PROTECTED]> wrote: > >>> Off topic, as I seldom partition anything (unpartitioned drives > >>> perform best), but, you're setting yourself up for disaster using LVM > >>> (any corruption to the LVM layer is not recoverable... you'll loose > >>> everything... been there done that), and the performance is poor, and > >>> MD RAID5/6 devices can be grown (add more disks). > >>> > >>> Chris > >>> > >> Fair enough. I appreciate the input because I haven't run across any > >> real-world stories about LVM corruption. I have personally encountered > >> corruption problems with RAID5/6 as well as problems with decreased > >> performance as a RAID5 structure gets more members added to it. > > > > I saw some RAID6 issues last year, so I use RAID5... but recent tests > > have shown MD RAID6 as solid. > > > > "Decreased performance as more members get added to it"? Bull!!! I'm > > guessing you have another bottleneck that has led you to this > > conclusion. > > > > While the performance increase doesn't scale linearly as disks are > > added (some CPU verhead is added with each additional drive), the more > > disks, the better the performance. I'm sure there is some Amdahl's > > law limit to the increased performance scalability, but I run RAIDS up > > to 12 drives, and see performance added w/ each new member. > > > > You're hallucinating. That defies basic information theory. > > Your assertion is akin to suggesting that you power your > computers with a perpetual motion machine (despite the > fact that such would violate the 1st, 2nd, and 3rd laws > of thermodynamics).
Single threaded access to a raid array may not be helped by adding drives. Drive access can end up being sequential and your not really buying anything. Multi-threaded storage performance is definitely positively affected by adding disks to an array. For multi-threaded, effectively each disk can do N IOPS (IOs per Second.) So if you have M drives, you can do M*N IOPS. The trouble with Raid 5 is that it typically requires 4 IOs to update a single sector. ie. Read checksum, Read original sector, (so you can remove it from the checksum) write updated sector write new checksum. So it ends up being M*N / 4 IOPS. So from a performance perspective on _writes_ you need at least a 4 drive array just to be as fast as a single disk. Reads OTOH just need to read the sector they want (unless you have a failed drive). So _read_ performance is M*N. Or always faster than a single drive. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
