Hands-On Testing and Analysis

Talking Data Protection – Here and at vBrownBag

Water Cooler Raid E1513047547352

Now that we’ve finished talking about RAID it seemed like a good time to both recap and announce that our friends at vBrownBag have asked me to turn this little series of blog posts into a month of vBrownbag webinars this January. Why Talk RAID in 2017? I was inspired, OK obsessed, to write this series returning to first principles …

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All About Data Protection Part 6 ½ – Thinking About Parity and Read-Modify-Write


In part 3 of this series, I described how single parity RAID, levels 4 and 5 for those keeping track at home, worked. In that post, I talked about the I/O expansion, and performance penalty created by the read-modify-write process that’s required for writes smaller than the size of a full RAID stripe. In that post I wrote, “RAID4 performs …

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All About Data Protection Part 6 – Nested and Combination RAID

Raid 61

While the basic RAID level concepts addressed some of our concerns about disk drive performance and reliability they are all really just the most basic building blocks of data protection. Users, and vendors, needing RAID sets bigger than, or with higher resiliency than, the standard RAID levels can deliver have built some amazing combinations to address their particular problems. The …

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All About Data Protection Part 5 – From Patterson to Products

Flash Drive RAID Array 300x203

I read an interview with Randy Katz of the original RAID paper where he said the academics initially thought that RAID would be used as a performance solution aggregating the performance of many spindles. He went on to say that they were surprised that it was the file server crowd who couldn’t afford more reliable drives, which cost 10X or …

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All About Data Protection Part IV – RAID6 – Double The Parity, Double The Fun

Belt And Suspenders

In today’s episode our hero, always searching for ever higher levels of resiliency, adds a second parity strip, sticks a feather in his cap and calls it RAID6. RAID5 systems protect user data against a single device failure, but leave data vulnerable to multiple device failures and more significantly read failures from otherwise working drives during a rebuild. RAID6 technologies …

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The Data Protection Diaries Part 3 – Parity RAID

Raid 3

In this installment of As the Disk Drive Turns, we’ll explore RAID levels two through five and the math(s) they use to protect data with less overhead than mirroring. RAID2 and RAID3 Bits and Bytes Not Blocks RAID2 stripes data across multiple drives at the bit level using Hamming codes. RAID3 uses parity but at the byte, not block level. …

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All About Data Protection Part 2¾ – A Few Words On Parity


Unfortunately, parity is one of those words that means different things depending on the context. To make things worse we IT folks talk about double-parity, a concept that would make our favorite mathematician, Rachel Traylor Ph.D., blow her top. Strictly speaking, parity is the special case of a forward error correction code, which adds one error check bit to some …

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All About Data Protection – Part 2 How RAID Works, Stripes and Mirrors


Here’s how storage systems use the concepts of RAID to protect your data. In A Case for Redundant Arrays of Inexpensive Disks, Patterson, Gibson and Katz propose five methods for using arrays of slow, unreliable but inexpensive drives to match the performance and reliability of the SLEDs (Single Large Expensive Disks) then dominating the minicomputer and mainframe storage market. They …

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All About Data Protection – Part One Where Did RAID Come From?


Just about all modern data protection schemes divide data into some arbitrarily sized block. Then, they either duplicate that block across multiple storage devices, or store portions of that data block, which we’ll call strips, in stripes across multiple storage devices, with one or more additional strips in each stripe containing parity or other erasure code data. Those are pretty …

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Notes from the NAND Front


I ran across an interesting article on the site about the state of the NAND flash market. While much of the article covers trends I wrote about in a post at SearchSolidStateStorage like the difficulty vendors have had in ramping up 3D NAND production there were a few tidbits I thought you, my dear readers, would be interested in. The first …

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