On Sat, Mar 6, 2010 at 3:17 PM, Guy Watkins <linux-raid@xxxxxxxxxxxxxxxx> wrote: > } -----Original Message----- > } From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- > } owner@xxxxxxxxxxxxxxx] On Behalf Of Greg Freemyer > } Sent: Saturday, March 06, 2010 5:33 PM > } To: Mark Knecht > } Cc: Linux-RAID > } Subject: Re: What RAID type and why? > } > } On Sat, Mar 6, 2010 at 5:02 PM, Mark Knecht <markknecht@xxxxxxxxx> wrote: > } > First post. I've never used RAID but am thinking about it and looking > } > for newbie-level info. Thanks in advance. > } > > } > I'm thinking about building a machine for long term number crunching > } > of stock market data. Highest end processor I can get, 16GB and at > } > least reasonably fast drives. I've not done RAID before and don't know > } > how to choose one RAID type over another for this sort of workload. > } > All I know is I want the machine to run 24/7 computing 100% of the > } > time and be reliable at least in the sense of not losing data if 1 > } > drive or possibly 2 go down. > } > > } > If a drive does go down I'm not overly worried about down time. I'll > } > stock a couple of spares when I build the machine and power the box > } > back up within an hour or two. > } > > } > What RAID type do I choose and why? > } > > } > Do I need a 5 physical drive RAID array to meet these requirements? > } > Assume 1TB+ drives all around. > } > > } > How critical is it going forward with Linux RAID solutions to be able > } > to get exactly the same drives in the future? 1TB today is 4TB a year > } > from now, etc. > } > > } > With an 8 core processor (high-end Intel Core i7 probably) do I need > } > to worry much about CPU usage doing RAID? I suspect not and I don't > } > really want to get into hardware RAID controllers unless critically > } > necessary which I suspect it isn't. > } > > } > Anyway, if there's a document around somewhere that helps a newbie > } > like me I'd sure appreciate finding out about it. > } > > } > Thanks, > } > Mark > } > } I'm not sure about a newbie doc, but here's some basics: > } > } You haven't said what kind of i/o rates you expect, nor how much > } storage you need. > } > } At a minimum I would build a 3-disk raid 6. raid 6 does a lot of i/o > } which may be a problem. > > If he only needs 3 drives I would recommend RAID1. Can still loose 2 drives > and you don't have the RAID6 I/O overhead. > > Also, you said your data is important. If so, you need a backup solution! > 2 copies with 1 off-site. Maybe alternate between the 2 each day or week. > > How much data per day? How much data during the next 3 years? > > Guy > > } > } Raid-5 is out of favor for me due to issues people are seeing with > } discrete bad sectors with the remaining drives after you have a drive > } failure. raid-6 tolerates those much better. Even raid 10 is not as > } robust as raid 6 and with the current generation drives robustness in > } the raid solution is more important than ever. > } > } But raid 6 uses 2 parity drives, so you'll only get 1TB of useable > } space from a 3-disk raid 6 made from 1TB drives. > } > } mdraid just requires replacement disks be bigger than the old disk > } you're replacing. > } > } You might consider layering LVM on top of mdraid to help you manage > } the array as it grows. > } > } 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 > > -- > 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 > More importantly, it sounds like his workload will be mostly /database/ driven. As far as I'm aware, databases tend to produce many small operations; which unfortunately pushes favor to the simple mirroring operations. If two drives going bad is a concern then using 2 backup copies per raid 1 mirror set would work. Most modern consumer systems come with 6 SATA ports or more, so it should be possible to get 6 hard drives installed and shared among two raid 1 sets of 3 drives each. LVM with striping could be used over the raid 1 sets. On the other hand, he says that the system will have 16 GB of memory; I'm not sure what size his working set is, but it sounds entirely plausible that a well constructed database could live entirely within the ram. If that's the case it doesn't really matter what the precise performance of the storage solution is. Raid 6 would offer more efficient drive use at similar rates of error tolerance at a cost savings of 2 drives in the six drive case. Update for new email: Just go with the raid 1 version; it sounds like you aren't trying to store terabytes of data so the raid 1 solution with even just 3 drives should be sufficient. Put the saved resources in to more, faster, or better memory. -- 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
