Thank you for the feedback on the disks, I have found a VDI Calculator http://myvirtualcloud.net/?page_id=1076 that supports the notion that I am heavy on the storage capacity. Yes, SAS drives not SATA drives. His storage size chart is at http://myvirtualcloud.net/?p=779.
This tool provides actual numbers to the IOPs when changing from RAID5, RAID6 and RAID10. His IOPs article is http://myvirtualcloud.net/?p=1421 I have read a great deal about storage sizing and IOPs, but almost every article tells me to start with my first machine and see how it's being used in my environment. I think the first machine will likely have to be a bit overkill to ensure we can use it, then get real data and purchase the next machine off of known data. On Fri, Jul 5, 2013 at 2:51 PM, Kurt Buff <[email protected]> wrote: > On Fri, Jul 5, 2013 at 11:20 AM, Ben Scott <[email protected]> wrote: > > On Fri, Jul 5, 2013 at 1:37 PM, David Lum <[email protected]> wrote: > >>> Be careful of a SATA Raid array. I've got a couple of these and in an > >>> effort to save money and I'm not doing it again. The issue comes down > to > >>> something I learned about the hard way. "Array Puncture"... > >> > >> I have never heard this term before today, looking it up now. > > > > Me neither. This explains it: > > > > > http://www.dell.com/support/troubleshooting/us/en/04/KCS/KcsArticles/ArticleView?c=us&l=en&s=bsd&docid=438291 > > > > Nothing to do with SATA, it appears. > > > > It's just a fallback method for a double fault. A double fault is > > when two blocks (stripes) are both found to be bad. This is more than > > a RAID 5 can tolerate. A "puncture" appears to just be an option to > > keep an array operating despite a double fault. You've got two > > choices when you encounter a double fault, fail the entire array > > offline, or "puncture" it, rebuilding what you can, and returning > > error on those particular blocks. > > > > The double fault problem has been known for decades, and is why > > better RAID implementations do regular consistency checks across all > > disk members. > > > > -- Ben > > Two things to add to that: > > o- RAID 6 is more resilient, but of course the controllers cost more, > and there is a performance penalty vs. other RAID categories, which > better ($) controllers can mitigate. > > o- Larger arrays (whether made up of larger disks or larger numbers of > disks, or both) will have more errors, and therefore a higher > probability of simultaneous errors, than smaller arrays. They are also > slower to perform consistency scans against. > > So, having said that, I'm of the opinion that a RAID 5 array of 16 x > 300gb drives is probably OK for RAID 5, especially if one of them is a > dedicated hot spare. I haven't done the math to back that up, but in > the world of 3.5" drives it's been pretty reasonable. Don't know about > OPs situation, as he's considering 2.5" drives, though a quick search > of CDW reveals that 300gb, 2.5", 10k rpm SATA drives don't exist - > although they have them in SAS and SAS-2, in both 10k and 15k speeds. > > Kurt > > >
