Category Archive for: ‘Data Protection Tutorial’

Hard Drive Evolution Part IV


When we last saw our hero the hard drive he had shrunk down to what we now call the large form factor with a 3.5” case with the higher performance 10,000 and 15,000 RPM drives using even smaller platters to keep their power consumption under control. Features that used to be limited to high-performance drives like voice coil positioners and …

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Hard Drive Evolution Part 3


Stepper Motors to Voice Coils The first 5 ¼” hard drives like the ST-506, used a stepper motor to move the heads in and out. The head carriage was attached to a split steel band so each step of the motor in or out would define a track. Stepper motors were cheap, but even by the measure of those washing …

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The Evolution of the Disk Drive – Part II

Evolution Of HDD

In part one we took a brief look at the large, expensive disk drives of the past and saw how all of today’s disk drives can be considered descendants of the first 5 1/4″ HDD Seagate’s ST-506.  While the ST-506 itself was obsolete by the time the IBM PC hit the street the ST-506 interface dominated the first few years of …

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Hard Drive Evolution – Part I

Evolution Of Man

Since RAID was originally designed to parallelize disk drives for performance and resiliency, it seems pretty obvious that data protection techniques like RAID are constrained by the technology of the disk, and later solid state, drives they protect. It seems appropriate at this point to take a brief detour from explaining how we protect data from problems with disk drives …

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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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